strictNullChecks: `undefined` is not assignable to type script

[alan-agius4]

TypeScript Version: 2.4.1

Code

if (process.env.npm_config_argv !== undefined) {
const x = JSON.parse(process.env.npm_config_argv);
....
}

Expected behavior:
no errors as i am already doing a check

Actual behavior:
error TS2345: Argument of type 'string | undefined' is not assignable to parameter of type 'string'.
Type 'undefined' is not assignable to type 'string'.

[sylvanaar]

This is fixed in the current dev build.

#15796

[xfoxfu]

No, I have got the latest dev build 2.5.0-dev.20170807 and still found the bug occurring.

const log = (data: string) => console.log(data);
if (process.env.npm_config_argv !== undefined) {
  log(process.env.npm_config_argv);
}

temp.ts(3,7): error TS2345: Argument of type 'string | undefined' is not assignable to parameter of type 'string'.
  Type 'undefined' is not assignable to type 'string'.

[kitsonk]

It appears that index based types are not tracked when accessed, only explicit properties.

// @strictNullChecks: true

declare const foo: { [key: string]: string | undefined; baz: string | undefined; };

if (foo.bar) {
  foo.bar; // string | undefined
}

if (foo.baz) {
  foo.baz; // string
}

[RyanCavanaugh]

Duplicate of #17567

[mhegazy]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.