diff --git a/src/compiler/binder.ts b/src/compiler/binder.ts
index 52f99bcb8d7..6ffe3a7ef52 100644
--- a/src/compiler/binder.ts
+++ b/src/compiler/binder.ts
@@ -850,6 +850,9 @@ namespace ts {
                 case SyntaxKind.BindingElement:
                     bindBindingElementFlow(node as BindingElement);
                     break;
+                case SyntaxKind.Parameter:
+                    bindParameterFlow(node as ParameterDeclaration);
+                    break;
                 case SyntaxKind.ObjectLiteralExpression:
                 case SyntaxKind.ArrayLiteralExpression:
                 case SyntaxKind.PropertyAssignment:
@@ -1655,20 +1658,40 @@ namespace ts {
         }
 
         function bindBindingElementFlow(node: BindingElement) {
-            if (isBindingPattern(node.name)) {
-                // When evaluating a binding pattern, the initializer is evaluated before the binding pattern, per:
-                // - https://tc39.es/ecma262/#sec-destructuring-binding-patterns-runtime-semantics-iteratorbindinginitialization
-                //   - `BindingElement: BindingPattern Initializer?`
-                // - https://tc39.es/ecma262/#sec-runtime-semantics-keyedbindinginitialization
-                //   - `BindingElement: BindingPattern Initializer?`
-                bind(node.dotDotDotToken);
-                bind(node.propertyName);
-                bind(node.initializer);
-                bind(node.name);
+            // When evaluating a binding pattern, the initializer is evaluated before the binding pattern, per:
+            // - https://tc39.es/ecma262/#sec-destructuring-binding-patterns-runtime-semantics-iteratorbindinginitialization
+            //   - `BindingElement: BindingPattern Initializer?`
+            // - https://tc39.es/ecma262/#sec-runtime-semantics-keyedbindinginitialization
+            //   - `BindingElement: BindingPattern Initializer?`
+            bind(node.dotDotDotToken);
+            bind(node.propertyName);
+            bindInitializer(node.initializer);
+            bind(node.name);
+        }
+
+        function bindParameterFlow(node: ParameterDeclaration) {
+            bindEach(node.modifiers);
+            bind(node.dotDotDotToken);
+            bind(node.questionToken);
+            bind(node.type);
+            bindInitializer(node.initializer);
+            bind(node.name);
+        }
+
+        // a BindingElement/Parameter does not have side effects if initializers are not evaluated and used. (see GH#49759)
+        function bindInitializer(node: Expression | undefined) {
+            if (!node) {
+                return;
             }
-            else {
-                bindEachChild(node);
+            const entryFlow = currentFlow;
+            bind(node);
+            if (entryFlow === unreachableFlow || entryFlow === currentFlow) {
+                return;
             }
+            const exitFlow = createBranchLabel();
+            addAntecedent(exitFlow, entryFlow);
+            addAntecedent(exitFlow, currentFlow);
+            currentFlow = finishFlowLabel(exitFlow);
         }
 
         function bindJSDocTypeAlias(node: JSDocTypedefTag | JSDocCallbackTag | JSDocEnumTag) {
diff --git a/tests/baselines/reference/controlFlowBindingElement.js b/tests/baselines/reference/controlFlowBindingElement.js
new file mode 100644
index 00000000000..e08cb83372f
--- /dev/null
+++ b/tests/baselines/reference/controlFlowBindingElement.js
@@ -0,0 +1,136 @@
+//// [controlFlowBindingElement.ts]
+{
+    const data =  { param: 'value' };
+
+    const {
+        param = (() => { throw new Error('param is not defined') })(),
+    } = data;
+    
+    console.log(param); // should not trigger 'Unreachable code detected.'    
+}
+
+
+{
+    const data =  { param: 'value' };
+
+    let foo: string | undefined = "";
+    const {
+        param = (() => { throw new Error('param is not defined') })(),
+    } = data;
+    
+    foo;  // should be string  
+}
+
+{
+    const data =  { param: 'value' };
+
+    let foo: string | undefined = "";
+    const {
+        param = (() => { foo = undefined })(),
+    } = data;
+    
+    foo;  // should be string | undefined
+}
+
+{
+    const data =  { param: 'value' };
+
+    let foo: string | undefined = "";
+    const {
+        param = (() => { return "" + 1 })(),
+    } = data;
+    
+    foo;  // should be string
+}
+
+{
+    interface Window {
+        window: Window;
+    }
+
+    let foo: string | undefined;
+    let window = {} as Window;
+    window.window = window;
+
+    const { [(() => { foo = ""; return 'window' as const })()]:
+        { [(() => { return 'window' as const })()]: bar } } = window;
+
+    foo;  // should be string
+}
+
+{
+    interface Window {
+        window: Window;
+    }
+
+    let foo: string | undefined;
+    let window = {} as Window;
+    window.window = window;
+
+    const { [(() => {  return 'window' as const })()]:
+        { [(() => { foo = ""; return 'window' as const })()]: bar } } = window;
+
+    foo;  // should be string
+}
+
+{
+    interface Window {
+        window: Window;
+    }
+
+    let foo: string | undefined;
+    let window = {} as Window;
+    window.window = window;
+
+    const { [(() => { return 'window' as const })()]:
+        { [(() => { return 'window' as const })()]: bar = (() => { foo = ""; return window; })() } } = window;
+
+    foo;  // should be string | undefined
+}
+
+
+//// [controlFlowBindingElement.js]
+{
+    var data = { param: 'value' };
+    var _a = data.param, param = _a === void 0 ? (function () { throw new Error('param is not defined'); })() : _a;
+    console.log(param); // should not trigger 'Unreachable code detected.'    
+}
+{
+    var data = { param: 'value' };
+    var foo = "";
+    var _b = data.param, param = _b === void 0 ? (function () { throw new Error('param is not defined'); })() : _b;
+    foo; // should be string  
+}
+{
+    var data = { param: 'value' };
+    var foo_1 = "";
+    var _c = data.param, param = _c === void 0 ? (function () { foo_1 = undefined; })() : _c;
+    foo_1; // should be string | undefined
+}
+{
+    var data = { param: 'value' };
+    var foo = "";
+    var _d = data.param, param = _d === void 0 ? (function () { return "" + 1; })() : _d;
+    foo; // should be string
+}
+{
+    var foo_2;
+    var window_1 = {};
+    window_1.window = window_1;
+    var _e = window_1, _f = (function () { foo_2 = ""; return 'window'; })(), _g = (function () { return 'window'; })(), bar = _e[_f][_g];
+    foo_2; // should be string
+}
+{
+    var foo_3;
+    var window_2 = {};
+    window_2.window = window_2;
+    var _h = window_2, _j = (function () { return 'window'; })(), _k = (function () { foo_3 = ""; return 'window'; })(), bar = _h[_j][_k];
+    foo_3; // should be string
+}
+{
+    var foo_4;
+    var window_3 = {};
+    window_3.window = window_3;
+    var _l = window_3, _m = (function () { return 'window'; })(), _o = (function () { return 'window'; })(), _p = _l[_m][_o], bar = _p === void 0 ? (function () { foo_4 = ""; return window_3; })() : _p;
+    foo_4; // should be string | undefined
+}
diff --git a/tests/baselines/reference/controlFlowBindingElement.symbols b/tests/baselines/reference/controlFlowBindingElement.symbols
new file mode 100644
index 00000000000..683a8e2c7be
--- /dev/null
+++ b/tests/baselines/reference/controlFlowBindingElement.symbols
@@ -0,0 +1,188 @@
+=== tests/cases/conformance/controlFlow/controlFlowBindingElement.ts ===
+{
+    const data =  { param: 'value' };
+>data : Symbol(data, Decl(controlFlowBindingElement.ts, 1, 9))
+>param : Symbol(param, Decl(controlFlowBindingElement.ts, 1, 19))
+
+    const {
+        param = (() => { throw new Error('param is not defined') })(),
+>param : Symbol(param, Decl(controlFlowBindingElement.ts, 3, 11))
+>Error : Symbol(Error, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+    } = data;
+>data : Symbol(data, Decl(controlFlowBindingElement.ts, 1, 9))
+    
+    console.log(param); // should not trigger 'Unreachable code detected.'    
+>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
+>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>param : Symbol(param, Decl(controlFlowBindingElement.ts, 3, 11))
+}
+
+
+{
+    const data =  { param: 'value' };
+>data : Symbol(data, Decl(controlFlowBindingElement.ts, 12, 9))
+>param : Symbol(param, Decl(controlFlowBindingElement.ts, 12, 19))
+
+    let foo: string | undefined = "";
+>foo : Symbol(foo, Decl(controlFlowBindingElement.ts, 14, 7))
+
+    const {
+        param = (() => { throw new Error('param is not defined') })(),
+>param : Symbol(param, Decl(controlFlowBindingElement.ts, 15, 11))
+>Error : Symbol(Error, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+    } = data;
+>data : Symbol(data, Decl(controlFlowBindingElement.ts, 12, 9))
+    
+    foo;  // should be string  
+>foo : Symbol(foo, Decl(controlFlowBindingElement.ts, 14, 7))
+}
+
+{
+    const data =  { param: 'value' };
+>data : Symbol(data, Decl(controlFlowBindingElement.ts, 23, 9))
+>param : Symbol(param, Decl(controlFlowBindingElement.ts, 23, 19))
+
+    let foo: string | undefined = "";
+>foo : Symbol(foo, Decl(controlFlowBindingElement.ts, 25, 7))
+
+    const {
+        param = (() => { foo = undefined })(),
+>param : Symbol(param, Decl(controlFlowBindingElement.ts, 26, 11))
+>foo : Symbol(foo, Decl(controlFlowBindingElement.ts, 25, 7))
+>undefined : Symbol(undefined)
+
+    } = data;
+>data : Symbol(data, Decl(controlFlowBindingElement.ts, 23, 9))
+    
+    foo;  // should be string | undefined
+>foo : Symbol(foo, Decl(controlFlowBindingElement.ts, 25, 7))
+}
+
+{
+    const data =  { param: 'value' };
+>data : Symbol(data, Decl(controlFlowBindingElement.ts, 34, 9))
+>param : Symbol(param, Decl(controlFlowBindingElement.ts, 34, 19))
+
+    let foo: string | undefined = "";
+>foo : Symbol(foo, Decl(controlFlowBindingElement.ts, 36, 7))
+
+    const {
+        param = (() => { return "" + 1 })(),
+>param : Symbol(param, Decl(controlFlowBindingElement.ts, 37, 11))
+
+    } = data;
+>data : Symbol(data, Decl(controlFlowBindingElement.ts, 34, 9))
+    
+    foo;  // should be string
+>foo : Symbol(foo, Decl(controlFlowBindingElement.ts, 36, 7))
+}
+
+{
+    interface Window {
+>Window : Symbol(Window, Decl(controlFlowBindingElement.ts, 44, 1))
+
+        window: Window;
+>window : Symbol(Window.window, Decl(controlFlowBindingElement.ts, 45, 22))
+>Window : Symbol(Window, Decl(controlFlowBindingElement.ts, 44, 1))
+    }
+
+    let foo: string | undefined;
+>foo : Symbol(foo, Decl(controlFlowBindingElement.ts, 49, 7))
+
+    let window = {} as Window;
+>window : Symbol(window, Decl(controlFlowBindingElement.ts, 50, 7))
+>Window : Symbol(Window, Decl(controlFlowBindingElement.ts, 44, 1))
+
+    window.window = window;
+>window.window : Symbol(Window.window, Decl(controlFlowBindingElement.ts, 45, 22))
+>window : Symbol(window, Decl(controlFlowBindingElement.ts, 50, 7))
+>window : Symbol(Window.window, Decl(controlFlowBindingElement.ts, 45, 22))
+>window : Symbol(window, Decl(controlFlowBindingElement.ts, 50, 7))
+
+    const { [(() => { foo = ""; return 'window' as const })()]:
+>foo : Symbol(foo, Decl(controlFlowBindingElement.ts, 49, 7))
+>const : Symbol(const)
+
+        { [(() => { return 'window' as const })()]: bar } } = window;
+>const : Symbol(const)
+>bar : Symbol(bar, Decl(controlFlowBindingElement.ts, 54, 9))
+>window : Symbol(window, Decl(controlFlowBindingElement.ts, 50, 7))
+
+    foo;  // should be string
+>foo : Symbol(foo, Decl(controlFlowBindingElement.ts, 49, 7))
+}
+
+{
+    interface Window {
+>Window : Symbol(Window, Decl(controlFlowBindingElement.ts, 59, 1))
+
+        window: Window;
+>window : Symbol(Window.window, Decl(controlFlowBindingElement.ts, 60, 22))
+>Window : Symbol(Window, Decl(controlFlowBindingElement.ts, 59, 1))
+    }
+
+    let foo: string | undefined;
+>foo : Symbol(foo, Decl(controlFlowBindingElement.ts, 64, 7))
+
+    let window = {} as Window;
+>window : Symbol(window, Decl(controlFlowBindingElement.ts, 65, 7))
+>Window : Symbol(Window, Decl(controlFlowBindingElement.ts, 59, 1))
+
+    window.window = window;
+>window.window : Symbol(Window.window, Decl(controlFlowBindingElement.ts, 60, 22))
+>window : Symbol(window, Decl(controlFlowBindingElement.ts, 65, 7))
+>window : Symbol(Window.window, Decl(controlFlowBindingElement.ts, 60, 22))
+>window : Symbol(window, Decl(controlFlowBindingElement.ts, 65, 7))
+
+    const { [(() => {  return 'window' as const })()]:
+>const : Symbol(const)
+
+        { [(() => { foo = ""; return 'window' as const })()]: bar } } = window;
+>foo : Symbol(foo, Decl(controlFlowBindingElement.ts, 64, 7))
+>const : Symbol(const)
+>bar : Symbol(bar, Decl(controlFlowBindingElement.ts, 69, 9))
+>window : Symbol(window, Decl(controlFlowBindingElement.ts, 65, 7))
+
+    foo;  // should be string
+>foo : Symbol(foo, Decl(controlFlowBindingElement.ts, 64, 7))
+}
+
+{
+    interface Window {
+>Window : Symbol(Window, Decl(controlFlowBindingElement.ts, 74, 1))
+
+        window: Window;
+>window : Symbol(Window.window, Decl(controlFlowBindingElement.ts, 75, 22))
+>Window : Symbol(Window, Decl(controlFlowBindingElement.ts, 74, 1))
+    }
+
+    let foo: string | undefined;
+>foo : Symbol(foo, Decl(controlFlowBindingElement.ts, 79, 7))
+
+    let window = {} as Window;
+>window : Symbol(window, Decl(controlFlowBindingElement.ts, 80, 7))
+>Window : Symbol(Window, Decl(controlFlowBindingElement.ts, 74, 1))
+
+    window.window = window;
+>window.window : Symbol(Window.window, Decl(controlFlowBindingElement.ts, 75, 22))
+>window : Symbol(window, Decl(controlFlowBindingElement.ts, 80, 7))
+>window : Symbol(Window.window, Decl(controlFlowBindingElement.ts, 75, 22))
+>window : Symbol(window, Decl(controlFlowBindingElement.ts, 80, 7))
+
+    const { [(() => { return 'window' as const })()]:
+>const : Symbol(const)
+
+        { [(() => { return 'window' as const })()]: bar = (() => { foo = ""; return window; })() } } = window;
+>const : Symbol(const)
+>bar : Symbol(bar, Decl(controlFlowBindingElement.ts, 84, 9))
+>foo : Symbol(foo, Decl(controlFlowBindingElement.ts, 79, 7))
+>window : Symbol(window, Decl(controlFlowBindingElement.ts, 80, 7))
+>window : Symbol(window, Decl(controlFlowBindingElement.ts, 80, 7))
+
+    foo;  // should be string | undefined
+>foo : Symbol(foo, Decl(controlFlowBindingElement.ts, 79, 7))
+}
+
diff --git a/tests/baselines/reference/controlFlowBindingElement.types b/tests/baselines/reference/controlFlowBindingElement.types
new file mode 100644
index 00000000000..8c9c6ac79a5
--- /dev/null
+++ b/tests/baselines/reference/controlFlowBindingElement.types
@@ -0,0 +1,250 @@
+=== tests/cases/conformance/controlFlow/controlFlowBindingElement.ts ===
+{
+    const data =  { param: 'value' };
+>data : { param: string; }
+>{ param: 'value' } : { param: string; }
+>param : string
+>'value' : "value"
+
+    const {
+        param = (() => { throw new Error('param is not defined') })(),
+>param : string
+>(() => { throw new Error('param is not defined') })() : never
+>(() => { throw new Error('param is not defined') }) : () => never
+>() => { throw new Error('param is not defined') } : () => never
+>new Error('param is not defined') : Error
+>Error : ErrorConstructor
+>'param is not defined' : "param is not defined"
+
+    } = data;
+>data : { param: string; }
+    
+    console.log(param); // should not trigger 'Unreachable code detected.'    
+>console.log(param) : void
+>console.log : (...data: any[]) => void
+>console : Console
+>log : (...data: any[]) => void
+>param : string
+}
+
+
+{
+    const data =  { param: 'value' };
+>data : { param: string; }
+>{ param: 'value' } : { param: string; }
+>param : string
+>'value' : "value"
+
+    let foo: string | undefined = "";
+>foo : string | undefined
+>"" : ""
+
+    const {
+        param = (() => { throw new Error('param is not defined') })(),
+>param : string
+>(() => { throw new Error('param is not defined') })() : never
+>(() => { throw new Error('param is not defined') }) : () => never
+>() => { throw new Error('param is not defined') } : () => never
+>new Error('param is not defined') : Error
+>Error : ErrorConstructor
+>'param is not defined' : "param is not defined"
+
+    } = data;
+>data : { param: string; }
+    
+    foo;  // should be string  
+>foo : string
+}
+
+{
+    const data =  { param: 'value' };
+>data : { param: string; }
+>{ param: 'value' } : { param: string; }
+>param : string
+>'value' : "value"
+
+    let foo: string | undefined = "";
+>foo : string | undefined
+>"" : ""
+
+    const {
+        param = (() => { foo = undefined })(),
+>param : string | void
+>(() => { foo = undefined })() : void
+>(() => { foo = undefined }) : () => void
+>() => { foo = undefined } : () => void
+>foo = undefined : undefined
+>foo : string | undefined
+>undefined : undefined
+
+    } = data;
+>data : { param: string; }
+    
+    foo;  // should be string | undefined
+>foo : string | undefined
+}
+
+{
+    const data =  { param: 'value' };
+>data : { param: string; }
+>{ param: 'value' } : { param: string; }
+>param : string
+>'value' : "value"
+
+    let foo: string | undefined = "";
+>foo : string | undefined
+>"" : ""
+
+    const {
+        param = (() => { return "" + 1 })(),
+>param : string
+>(() => { return "" + 1 })() : string
+>(() => { return "" + 1 }) : () => string
+>() => { return "" + 1 } : () => string
+>"" + 1 : string
+>"" : ""
+>1 : 1
+
+    } = data;
+>data : { param: string; }
+    
+    foo;  // should be string
+>foo : string
+}
+
+{
+    interface Window {
+        window: Window;
+>window : Window
+    }
+
+    let foo: string | undefined;
+>foo : string | undefined
+
+    let window = {} as Window;
+>window : Window
+>{} as Window : Window
+>{} : {}
+
+    window.window = window;
+>window.window = window : Window
+>window.window : Window
+>window : Window
+>window : Window
+>window : Window
+
+    const { [(() => { foo = ""; return 'window' as const })()]:
+>(() => { foo = ""; return 'window' as const })() : "window"
+>(() => { foo = ""; return 'window' as const }) : () => "window"
+>() => { foo = ""; return 'window' as const } : () => "window"
+>foo = "" : ""
+>foo : string | undefined
+>"" : ""
+>'window' as const : "window"
+>'window' : "window"
+
+        { [(() => { return 'window' as const })()]: bar } } = window;
+>(() => { return 'window' as const })() : "window"
+>(() => { return 'window' as const }) : () => "window"
+>() => { return 'window' as const } : () => "window"
+>'window' as const : "window"
+>'window' : "window"
+>bar : Window
+>window : Window
+
+    foo;  // should be string
+>foo : string
+}
+
+{
+    interface Window {
+        window: Window;
+>window : Window
+    }
+
+    let foo: string | undefined;
+>foo : string | undefined
+
+    let window = {} as Window;
+>window : Window
+>{} as Window : Window
+>{} : {}
+
+    window.window = window;
+>window.window = window : Window
+>window.window : Window
+>window : Window
+>window : Window
+>window : Window
+
+    const { [(() => {  return 'window' as const })()]:
+>(() => {  return 'window' as const })() : "window"
+>(() => {  return 'window' as const }) : () => "window"
+>() => {  return 'window' as const } : () => "window"
+>'window' as const : "window"
+>'window' : "window"
+
+        { [(() => { foo = ""; return 'window' as const })()]: bar } } = window;
+>(() => { foo = ""; return 'window' as const })() : "window"
+>(() => { foo = ""; return 'window' as const }) : () => "window"
+>() => { foo = ""; return 'window' as const } : () => "window"
+>foo = "" : ""
+>foo : string | undefined
+>"" : ""
+>'window' as const : "window"
+>'window' : "window"
+>bar : Window
+>window : Window
+
+    foo;  // should be string
+>foo : string
+}
+
+{
+    interface Window {
+        window: Window;
+>window : Window
+    }
+
+    let foo: string | undefined;
+>foo : string | undefined
+
+    let window = {} as Window;
+>window : Window
+>{} as Window : Window
+>{} : {}
+
+    window.window = window;
+>window.window = window : Window
+>window.window : Window
+>window : Window
+>window : Window
+>window : Window
+
+    const { [(() => { return 'window' as const })()]:
+>(() => { return 'window' as const })() : "window"
+>(() => { return 'window' as const }) : () => "window"
+>() => { return 'window' as const } : () => "window"
+>'window' as const : "window"
+>'window' : "window"
+
+        { [(() => { return 'window' as const })()]: bar = (() => { foo = ""; return window; })() } } = window;
+>(() => { return 'window' as const })() : "window"
+>(() => { return 'window' as const }) : () => "window"
+>() => { return 'window' as const } : () => "window"
+>'window' as const : "window"
+>'window' : "window"
+>bar : Window
+>(() => { foo = ""; return window; })() : Window
+>(() => { foo = ""; return window; }) : () => Window
+>() => { foo = ""; return window; } : () => Window
+>foo = "" : ""
+>foo : string | undefined
+>"" : ""
+>window : Window
+>window : Window
+
+    foo;  // should be string | undefined
+>foo : string | undefined
+}
+
diff --git a/tests/baselines/reference/controlFlowBindingPatternOrder.errors.txt b/tests/baselines/reference/controlFlowBindingPatternOrder.errors.txt
new file mode 100644
index 00000000000..37b608c3071
--- /dev/null
+++ b/tests/baselines/reference/controlFlowBindingPatternOrder.errors.txt
@@ -0,0 +1,39 @@
+tests/cases/conformance/controlFlow/controlFlowBindingPatternOrder.ts(10,11): error TS2322: Type '0 | 9' is not assignable to type '9'.
+  Type '0' is not assignable to type '9'.
+tests/cases/conformance/controlFlow/controlFlowBindingPatternOrder.ts(25,11): error TS2322: Type '0 | 9 | 8' is not assignable to type '0 | 8'.
+  Type '9' is not assignable to type '0 | 8'.
+
+
+==== tests/cases/conformance/controlFlow/controlFlowBindingPatternOrder.ts (2 errors) ====
+    // https://github.com/microsoft/TypeScript/pull/41094#issuecomment-716044363
+    {
+        let a: 0 | 1 = 0;
+        const [{ [(a = 1)]: b } = [9, a] as const] = [];
+        const bb: 0 = b;
+    }
+    {
+        let a: 0 | 1 = 1;
+        const [{ [a]: b } = [9, a = 0] as const] = [];
+        const bb: 9 = b;
+              ~~
+!!! error TS2322: Type '0 | 9' is not assignable to type '9'.
+!!! error TS2322:   Type '0' is not assignable to type '9'.
+    }
+    {
+        let a: 0 | 1 | 2 = 1;
+        const [{ [a]: b } = [9, a = 0, 5] as const] = [];
+        const bb: 0 | 9 = b;
+    }
+    {
+        let a: 0 | 1 = 0;
+        const [{ [(a = 1)]: b } = [9, a] as const] = [[9, 8] as const];
+        const bb: 0 | 8 = b;
+    }
+    {
+        let a: 0 | 1 = 1;
+        const [{ [a]: b } = [a = 0, 9] as const] = [[8, 9] as const];
+        const bb: 0 | 8 = b;
+              ~~
+!!! error TS2322: Type '0 | 9 | 8' is not assignable to type '0 | 8'.
+!!! error TS2322:   Type '9' is not assignable to type '0 | 8'.
+    }
\ No newline at end of file
diff --git a/tests/baselines/reference/controlFlowBindingPatternOrder.symbols b/tests/baselines/reference/controlFlowBindingPatternOrder.symbols
index fea01b4d125..7791d4540e0 100644
--- a/tests/baselines/reference/controlFlowBindingPatternOrder.symbols
+++ b/tests/baselines/reference/controlFlowBindingPatternOrder.symbols
@@ -29,25 +29,24 @@
 >b : Symbol(b, Decl(controlFlowBindingPatternOrder.ts, 8, 12))
 }
 {
-    let a: 0 | 1 = 0;
+    let a: 0 | 1 | 2 = 1;
 >a : Symbol(a, Decl(controlFlowBindingPatternOrder.ts, 12, 7))
 
-    const [{ [(a = 1)]: b } = [9, a] as const] = [[9, 8] as const];
+    const [{ [a]: b } = [9, a = 0, 5] as const] = [];
 >a : Symbol(a, Decl(controlFlowBindingPatternOrder.ts, 12, 7))
 >b : Symbol(b, Decl(controlFlowBindingPatternOrder.ts, 13, 12))
 >a : Symbol(a, Decl(controlFlowBindingPatternOrder.ts, 12, 7))
->const : Symbol(const)
 >const : Symbol(const)
 
-    const bb: 0 | 8 = b;
+    const bb: 0 | 9 = b;
 >bb : Symbol(bb, Decl(controlFlowBindingPatternOrder.ts, 14, 9))
 >b : Symbol(b, Decl(controlFlowBindingPatternOrder.ts, 13, 12))
 }
 {
-    let a: 0 | 1 = 1;
+    let a: 0 | 1 = 0;
 >a : Symbol(a, Decl(controlFlowBindingPatternOrder.ts, 17, 7))
 
-    const [{ [a]: b } = [a = 0, 9] as const] = [[8, 9] as const];
+    const [{ [(a = 1)]: b } = [9, a] as const] = [[9, 8] as const];
 >a : Symbol(a, Decl(controlFlowBindingPatternOrder.ts, 17, 7))
 >b : Symbol(b, Decl(controlFlowBindingPatternOrder.ts, 18, 12))
 >a : Symbol(a, Decl(controlFlowBindingPatternOrder.ts, 17, 7))
@@ -58,3 +57,18 @@
 >bb : Symbol(bb, Decl(controlFlowBindingPatternOrder.ts, 19, 9))
 >b : Symbol(b, Decl(controlFlowBindingPatternOrder.ts, 18, 12))
 }
+{
+    let a: 0 | 1 = 1;
+>a : Symbol(a, Decl(controlFlowBindingPatternOrder.ts, 22, 7))
+
+    const [{ [a]: b } = [a = 0, 9] as const] = [[8, 9] as const];
+>a : Symbol(a, Decl(controlFlowBindingPatternOrder.ts, 22, 7))
+>b : Symbol(b, Decl(controlFlowBindingPatternOrder.ts, 23, 12))
+>a : Symbol(a, Decl(controlFlowBindingPatternOrder.ts, 22, 7))
+>const : Symbol(const)
+>const : Symbol(const)
+
+    const bb: 0 | 8 = b;
+>bb : Symbol(bb, Decl(controlFlowBindingPatternOrder.ts, 24, 9))
+>b : Symbol(b, Decl(controlFlowBindingPatternOrder.ts, 23, 12))
+}
diff --git a/tests/baselines/reference/controlFlowBindingPatternOrder.types b/tests/baselines/reference/controlFlowBindingPatternOrder.types
index 5c9d426c23b..dd7e782885b 100644
--- a/tests/baselines/reference/controlFlowBindingPatternOrder.types
+++ b/tests/baselines/reference/controlFlowBindingPatternOrder.types
@@ -27,8 +27,8 @@
 >1 : 1
 
     const [{ [a]: b } = [9, a = 0] as const] = [];
->a : 0
->b : 9
+>a : 0 | 1
+>b : 0 | 9
 >[9, a = 0] as const : readonly [9, 0]
 >[9, a = 0] : readonly [9, 0]
 >9 : 9
@@ -39,7 +39,28 @@
 
     const bb: 9 = b;
 >bb : 9
->b : 9
+>b : 0 | 9
+}
+{
+    let a: 0 | 1 | 2 = 1;
+>a : 0 | 1 | 2
+>1 : 1
+
+    const [{ [a]: b } = [9, a = 0, 5] as const] = [];
+>a : 0 | 1
+>b : 0 | 9
+>[9, a = 0, 5] as const : readonly [9, 0, 5]
+>[9, a = 0, 5] : readonly [9, 0, 5]
+>9 : 9
+>a = 0 : 0
+>a : 0 | 1 | 2
+>0 : 0
+>5 : 5
+>[] : []
+
+    const bb: 0 | 9 = b;
+>bb : 0 | 9
+>b : 0 | 9
 }
 {
     let a: 0 | 1 = 0;
@@ -72,8 +93,8 @@
 >1 : 1
 
     const [{ [a]: b } = [a = 0, 9] as const] = [[8, 9] as const];
->a : 0
->b : 0 | 8
+>a : 0 | 1
+>b : 0 | 9 | 8
 >[a = 0, 9] as const : readonly [0, 9]
 >[a = 0, 9] : readonly [0, 9]
 >a = 0 : 0
@@ -88,5 +109,5 @@
 
     const bb: 0 | 8 = b;
 >bb : 0 | 8
->b : 0 | 8
+>b : 0 | 9 | 8
 }
diff --git a/tests/baselines/reference/controlFlowParameter.js b/tests/baselines/reference/controlFlowParameter.js
new file mode 100644
index 00000000000..283061f6650
--- /dev/null
+++ b/tests/baselines/reference/controlFlowParameter.js
@@ -0,0 +1,60 @@
+//// [controlFlowParameter.ts]
+function f1(
+  required: unknown = (() => {
+    throw new Error("bad");
+  })()
+) {
+  console.log("ok"); // should not trigger 'Unreachable code detected.'
+}
+
+function f2(
+  a: number | string | undefined,
+  required: unknown = (() => {
+    a = 1;
+  })()
+) {
+  a; // should be number | string | undefined
+}
+
+function f3(
+  a: number | string | undefined = 1,
+  required: unknown = (() => {
+    a = "";
+  })()
+) {
+  a; // should be number | string
+}
+
+function f4(
+  a: number | string | undefined = 1,
+  { [(a = "")]: b } = {} as any
+) {
+  a; // should be string
+}
+
+
+//// [controlFlowParameter.js]
+function f1(required) {
+    if (required === void 0) { required = (function () {
+        throw new Error("bad");
+    })(); }
+    console.log("ok"); // should not trigger 'Unreachable code detected.'
+}
+function f2(a, required) {
+    if (required === void 0) { required = (function () {
+        a = 1;
+    })(); }
+    a; // should be number | string | undefined
+}
+function f3(a, required) {
+    if (a === void 0) { a = 1; }
+    if (required === void 0) { required = (function () {
+        a = "";
+    })(); }
+    a; // should be number | string
+}
+function f4(a, _a) {
+    if (a === void 0) { a = 1; }
+    var _b = _a === void 0 ? {} : _a, _c = (a = ""), b = _b[_c];
+    a; // should be string
+}
diff --git a/tests/baselines/reference/controlFlowParameter.symbols b/tests/baselines/reference/controlFlowParameter.symbols
new file mode 100644
index 00000000000..b2f58685a0c
--- /dev/null
+++ b/tests/baselines/reference/controlFlowParameter.symbols
@@ -0,0 +1,69 @@
+=== tests/cases/conformance/controlFlow/controlFlowParameter.ts ===
+function f1(
+>f1 : Symbol(f1, Decl(controlFlowParameter.ts, 0, 0))
+
+  required: unknown = (() => {
+>required : Symbol(required, Decl(controlFlowParameter.ts, 0, 12))
+
+    throw new Error("bad");
+>Error : Symbol(Error, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+  })()
+) {
+  console.log("ok"); // should not trigger 'Unreachable code detected.'
+>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
+>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+}
+
+function f2(
+>f2 : Symbol(f2, Decl(controlFlowParameter.ts, 6, 1))
+
+  a: number | string | undefined,
+>a : Symbol(a, Decl(controlFlowParameter.ts, 8, 12))
+
+  required: unknown = (() => {
+>required : Symbol(required, Decl(controlFlowParameter.ts, 9, 33))
+
+    a = 1;
+>a : Symbol(a, Decl(controlFlowParameter.ts, 8, 12))
+
+  })()
+) {
+  a; // should be number | string | undefined
+>a : Symbol(a, Decl(controlFlowParameter.ts, 8, 12))
+}
+
+function f3(
+>f3 : Symbol(f3, Decl(controlFlowParameter.ts, 15, 1))
+
+  a: number | string | undefined = 1,
+>a : Symbol(a, Decl(controlFlowParameter.ts, 17, 12))
+
+  required: unknown = (() => {
+>required : Symbol(required, Decl(controlFlowParameter.ts, 18, 37))
+
+    a = "";
+>a : Symbol(a, Decl(controlFlowParameter.ts, 17, 12))
+
+  })()
+) {
+  a; // should be number | string
+>a : Symbol(a, Decl(controlFlowParameter.ts, 17, 12))
+}
+
+function f4(
+>f4 : Symbol(f4, Decl(controlFlowParameter.ts, 24, 1))
+
+  a: number | string | undefined = 1,
+>a : Symbol(a, Decl(controlFlowParameter.ts, 26, 12))
+
+  { [(a = "")]: b } = {} as any
+>a : Symbol(a, Decl(controlFlowParameter.ts, 26, 12))
+>b : Symbol(b, Decl(controlFlowParameter.ts, 28, 3))
+
+) {
+  a; // should be string
+>a : Symbol(a, Decl(controlFlowParameter.ts, 26, 12))
+}
+
diff --git a/tests/baselines/reference/controlFlowParameter.types b/tests/baselines/reference/controlFlowParameter.types
new file mode 100644
index 00000000000..0a77f532f1b
--- /dev/null
+++ b/tests/baselines/reference/controlFlowParameter.types
@@ -0,0 +1,93 @@
+=== tests/cases/conformance/controlFlow/controlFlowParameter.ts ===
+function f1(
+>f1 : (required?: unknown) => void
+
+  required: unknown = (() => {
+>required : unknown
+>(() => {    throw new Error("bad");  })() : never
+>(() => {    throw new Error("bad");  }) : () => never
+>() => {    throw new Error("bad");  } : () => never
+
+    throw new Error("bad");
+>new Error("bad") : Error
+>Error : ErrorConstructor
+>"bad" : "bad"
+
+  })()
+) {
+  console.log("ok"); // should not trigger 'Unreachable code detected.'
+>console.log("ok") : void
+>console.log : (...data: any[]) => void
+>console : Console
+>log : (...data: any[]) => void
+>"ok" : "ok"
+}
+
+function f2(
+>f2 : (a: number | string | undefined, required?: unknown) => void
+
+  a: number | string | undefined,
+>a : string | number | undefined
+
+  required: unknown = (() => {
+>required : unknown
+>(() => {    a = 1;  })() : void
+>(() => {    a = 1;  }) : () => void
+>() => {    a = 1;  } : () => void
+
+    a = 1;
+>a = 1 : 1
+>a : string | number | undefined
+>1 : 1
+
+  })()
+) {
+  a; // should be number | string | undefined
+>a : string | number | undefined
+}
+
+function f3(
+>f3 : (a?: number | string | undefined, required?: unknown) => void
+
+  a: number | string | undefined = 1,
+>a : string | number | undefined
+>1 : 1
+
+  required: unknown = (() => {
+>required : unknown
+>(() => {    a = "";  })() : void
+>(() => {    a = "";  }) : () => void
+>() => {    a = "";  } : () => void
+
+    a = "";
+>a = "" : ""
+>a : string | number | undefined
+>"" : ""
+
+  })()
+) {
+  a; // should be number | string
+>a : string | number
+}
+
+function f4(
+>f4 : (a?: number | string | undefined, { [(a = "")]: b }?: any) => void
+
+  a: number | string | undefined = 1,
+>a : string | number | undefined
+>1 : 1
+
+  { [(a = "")]: b } = {} as any
+>(a = "") : ""
+>a = "" : ""
+>a : string | number | undefined
+>"" : ""
+>b : any
+>{} as any : any
+>{} : {}
+
+) {
+  a; // should be string
+>a : string
+}
+
diff --git a/tests/cases/conformance/controlFlow/controlFlowBindingElement.ts b/tests/cases/conformance/controlFlow/controlFlowBindingElement.ts
new file mode 100644
index 00000000000..153666f9433
--- /dev/null
+++ b/tests/cases/conformance/controlFlow/controlFlowBindingElement.ts
@@ -0,0 +1,90 @@
+// @strictNullChecks: true
+// @allowUnreachableCode: false
+{
+    const data =  { param: 'value' };
+
+    const {
+        param = (() => { throw new Error('param is not defined') })(),
+    } = data;
+    
+    console.log(param); // should not trigger 'Unreachable code detected.'    
+}
+
+
+{
+    const data =  { param: 'value' };
+
+    let foo: string | undefined = "";
+    const {
+        param = (() => { throw new Error('param is not defined') })(),
+    } = data;
+    
+    foo;  // should be string  
+}
+
+{
+    const data =  { param: 'value' };
+
+    let foo: string | undefined = "";
+    const {
+        param = (() => { foo = undefined })(),
+    } = data;
+    
+    foo;  // should be string | undefined
+}
+
+{
+    const data =  { param: 'value' };
+
+    let foo: string | undefined = "";
+    const {
+        param = (() => { return "" + 1 })(),
+    } = data;
+    
+    foo;  // should be string
+}
+
+{
+    interface Window {
+        window: Window;
+    }
+
+    let foo: string | undefined;
+    let window = {} as Window;
+    window.window = window;
+
+    const { [(() => { foo = ""; return 'window' as const })()]:
+        { [(() => { return 'window' as const })()]: bar } } = window;
+
+    foo;  // should be string
+}
+
+{
+    interface Window {
+        window: Window;
+    }
+
+    let foo: string | undefined;
+    let window = {} as Window;
+    window.window = window;
+
+    const { [(() => {  return 'window' as const })()]:
+        { [(() => { foo = ""; return 'window' as const })()]: bar } } = window;
+
+    foo;  // should be string
+}
+
+{
+    interface Window {
+        window: Window;
+    }
+
+    let foo: string | undefined;
+    let window = {} as Window;
+    window.window = window;
+
+    const { [(() => { return 'window' as const })()]:
+        { [(() => { return 'window' as const })()]: bar = (() => { foo = ""; return window; })() } } = window;
+
+    foo;  // should be string | undefined
+}
diff --git a/tests/cases/conformance/controlFlow/controlFlowBindingPatternOrder.ts b/tests/cases/conformance/controlFlow/controlFlowBindingPatternOrder.ts
index 804947c9b70..9bacc6b7eb4 100644
--- a/tests/cases/conformance/controlFlow/controlFlowBindingPatternOrder.ts
+++ b/tests/cases/conformance/controlFlow/controlFlowBindingPatternOrder.ts
@@ -12,6 +12,11 @@
     const [{ [a]: b } = [9, a = 0] as const] = [];
     const bb: 9 = b;
 }
+{
+    let a: 0 | 1 | 2 = 1;
+    const [{ [a]: b } = [9, a = 0, 5] as const] = [];
+    const bb: 0 | 9 = b;
+}
 {
     let a: 0 | 1 = 0;
     const [{ [(a = 1)]: b } = [9, a] as const] = [[9, 8] as const];
diff --git a/tests/cases/conformance/controlFlow/controlFlowParameter.ts b/tests/cases/conformance/controlFlow/controlFlowParameter.ts
new file mode 100644
index 00000000000..09972b5f6e0
--- /dev/null
+++ b/tests/cases/conformance/controlFlow/controlFlowParameter.ts
@@ -0,0 +1,34 @@
+// @strictNullChecks: true
+// @allowUnreachableCode: false
+function f1(
+  required: unknown = (() => {
+    throw new Error("bad");
+  })()
+) {
+  console.log("ok"); // should not trigger 'Unreachable code detected.'
+}
+
+function f2(
+  a: number | string | undefined,
+  required: unknown = (() => {
+    a = 1;
+  })()
+) {
+  a; // should be number | string | undefined
+}
+
+function f3(
+  a: number | string | undefined = 1,
+  required: unknown = (() => {
+    a = "";
+  })()
+) {
+  a; // should be number | string
+}
+
+function f4(
+  a: number | string | undefined = 1,
+  { [(a = "")]: b } = {} as any
+) {
+  a; // should be string
+}