Merge pull request #28951 from Microsoft/fixLibToIterableAndES5

Only use 'es2015.iterable' to avoid accidental es2015 feature usage.

src/compiler/core.ts

@@ -2165,6 +2165,10 @@ namespace ts {
     }
 
     export function fill<T>(length: number, cb: (index: number) => T): T[] {
-        return new Array(length).fill(0).map((_, i) => cb(i));
+        const result = Array<T>(length);
+        for (let i = 0; i < length; i++) {
+            result[i] = cb(i);
+        }
+        return result;
     }
 }

src/tsconfig-base.json

@@ -1,7 +1,7 @@
 {
     "compilerOptions": {
         "pretty": true,
-        "lib": ["es2015"],
+        "lib": ["es2015.iterable", "es5"],
         "target": "es5",
         "rootDir": ".",