Answer for TypeScript 3.4 and above It is not really possible to convert a union to a tuple in TypeScript, at least not in a way that behaves well. Unions are intended to be unordered, and tuples are inherently ordered, so even if you can manage to do it, the resulting tuples can behave in … Read more
You can read more about unknown in the PR or the RC announcement, but the gist of it is: [..] unknown which is the type-safe counterpart of any. Anything is assignable to unknown, but unknown isn’t assignable to anything but itself and any without a type assertion or a control flow based narrowing. Likewise, no … Read more
This is a bit of a quirk in how unions work in conjunction with excess property checks. {A:1, C: 3} is actually compatible with {C: number} except for excess property checks: const o = {A:1, C: 3}; const ok: {C: number} = o; // No direct literal assignment, no excess property checks const nok: {C: … Read more
UPDATE: Looks like the question title attracts people looking for a union of all possible property value types, analogous to the way keyof gives you the union of all possible property key types. Let’s help those people first. You can make a ValueOf analogous to keyof, by using indexed access types with keyof T as … Read more
Here are two other solutions When a module is not yours – try to install types from @types: npm install -D @types/module-name If the above install errors – try changing import statements to require: // import * as yourModuleName from ‘module-name’; const yourModuleName = require(‘module-name’);
Complementing @fetzz great answer. SHORT ANSWER TLDR; There are two common causes for this kind of error message. You are doing the first one (see below). Along with the text, I explain in rich detail what this error message wants to convey. CAUSE 1: In typescript, a concrete instance is not allowed to be assigned … Read more
2019 Update The current answers and the official documentation are outdated. And for those new to TypeScript, the terminology used isn’t clear without examples. Below is a list of up-to-date differences. 1. Objects / Functions Both can be used to describe the shape of an object or a function signature. But the syntax differs. Interface … Read more
As stated by drewmoore, the proper solution in this case is to manually trigger change detection for the current component. This is done using the detectChanges() method of the ChangeDetectorRef object (imported from angular2/core), or its markForCheck() method, which also makes any parent components update. Relevant example: import { Component, ChangeDetectorRef, AfterViewInit } from ‘angular2/core’ … Read more
I just found the answer to this in another Stack Overflow question’s answer. declare global { interface Window { MyNamespace: any; } } window.MyNamespace = window.MyNamespace || {}; Basically, you need to extend the existing window interface to tell it about your new property.
The current return type (string[]) is intentional. Why? Consider some type like this: interface Point { x: number; y: number; } You write some code like this: function fn(k: keyof Point) { if (k === “x”) { console.log(“X axis”); } else if (k === “y”) { console.log(“Y axis”); } else { throw new Error(“This is … Read more