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Type guards don't work on key/value objects #14957
Description
TypeScript Version: 2.2.2 with --strictNullChecks
Code
let test: string;
const obj1: {val: string|number} = {val: ''};
if (typeof obj1.val === 'string') {
test = obj1.val; // => Works fine
}
const obj2: {[k: string]: string|number} = {val: ''};
if (typeof obj2.val === 'string') {
test = obj2.val; // => Type 'string | number' is not assignable to type 'string'
}Expected behavior:
Type guards to work on key/value objects
Actual behavior:
Can't infer the correct type after check
Activity
RyanCavanaugh commentedon Apr 3, 2017
Interesting. This will likely require some architectural changes as we currently have no symbol to associate with the
.valproperty access and thus nothing to narrow by.RyanCavanaugh commentedon Jul 22, 2020
This works now