In JS, object literal with computed property has no index signature

[ajafff]

TypeScript Version: 3.1.0-dev.20180803

Search Terms:

Code

// @filename: test.js
// @strict: true

/*1*/
let empty = {};
empty.foo;

/*2*/
let key = Math.random();
let computed = {[key]: 1};
computed[key];

Expected behavior:

empty has no index signature.
computed has an index signature {[x: number]: number}.
There's no implicitAny error on the element access computed[key].

Actual behavior:

None of the object literals has an index signature. This causes the element access computed[key] to have an implicitAny error.

Note that this is not an error in a TS file.

Related Issues:
This is caused by @weswigham's PR #25996. I agree with not adding an implicit string index signature to every JS object literal. But not adding one where it makes sense just loses type information.

[weswigham]

Hm. We must have been disabling this in JS in favor of the fake index signature. Shouldn't be too difficult to fix - should just be a removal of a condition in checkObjectLiteral. Thanks for the report!