Can't set values in dictionaries using dot notation

[RuiNtD]

TypeScript Version:

1.8.7

Code

var foo: { [index: string]: string; } = {};
foo.bar = 'test';
foo['hello'] = 'world';

Expected behavior:
The code would compile and run without any errors.

Actual behavior:
Line 3 works while line 2 throws an error when compiling:
test.ts(2,5): error TS2339: Property 'bar' does not exist on type '{ [index: string]: string; }'.

[mhegazy]

#4345 (comment)