Given better error messages for iterated entities when not using --downlevelIteration

[wangzishi]

TypeScript Version: 2.3.3

Code

String.fromCharCode(...new Uint8Array(0));

Expected behavior:
I would expect there is no compile error.

Actual behavior:

I have to write this code:

String.fromCharCode(...Array.from(new Uint8Array(0)));

[mhegazy]

use --downlevelIteration.

e.g.:

tsc --downlevelIteration --lib es5,es2015.iterable a.ts

[DanielRosenwasser]

In cases where the value is iterable (i.e. has a Symbol.iterator), we should issue this error message

Type '{0}' can only be iterated through when using the '--downlevelIteration' flag.

[TomasHubelbauer]

For people who come here from search, for me, using "target": "es6" fixed this. Before I didn't have any target configuration in tsconfig.json. This is with TypeScript 2.8.1.

[felixhaeberle]

Changing "ES5" to "ES2015" fixed it for me.