var stuff: { [key: string]: string; } = {}; stuff[‘a’] = ”; // ok stuff[‘a’] = 4; // error // … or, if you’re using this a lot and don’t want to type so much … interface StringMap { [key: string]: string; } var stuff2: StringMap = { }; // same as above
All you have to do is define your result as a string array, like the following: const result : string[] = []; Without defining the array type, it by default will be never. So when you tried to add a string to it, it was a type mismatch, and so it threw the error you … Read more
Enums in TypeScript 0.9 are string+number based. You should not need type assertion for simple conversions: enum Color{ Red, Green } // To String var green: string = Color[Color.Green]; // To Enum / number var color : Color = Color[green]; Try it online I have documention about this and other Enum patterns in my OSS … Read more
TypeScript 2.0 has the readonly modifier: class MyClass { readonly myReadOnlyProperty = 1; myMethod() { console.log(this.myReadOnlyProperty); this.myReadOnlyProperty = 5; // error, readonly } } new MyClass().myReadOnlyProperty = 5; // error, readonly It’s not exactly a constant because it allows assignment in the constructor, but that’s most likely not a big deal. Alternative Solution An alternative … Read more
The “d.ts” file is used to provide typescript type information about an API that’s written in JavaScript. The idea is that you’re using something like jQuery or underscore, an existing javascript library. You want to consume those from your typescript code. Rather than rewriting jquery or underscore or whatever in typescript, you can instead write … Read more
Using a juggling-check, you can test both null and undefined in one hit: if (x == null) { If you use a strict-check, it will only be true for values set to null and won’t evaluate as true for undefined variables: if (x === null) { You can try this with various values using this … Read more
Index types It is possible to denote obj as any, but that defeats the whole purpose of using typescript. obj = {} implies obj is an Object. Marking it as any makes no sense. To accomplish the desired consistency an interface could be defined as follows. interface LooseObject { [key: string]: any } var obj: … 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’);
Sure. A function’s type consists of the types of its argument and its return type. Here we specify that the callback parameter’s type must be “function that accepts a number and returns type any“: class Foo { save(callback: (n: number) => any) : void { callback(42); } } var foo = new Foo(); var strCallback … Read more
TypeScript uses getter/setter syntax that is like ECMAScript4/ActionScript3. class foo { private _bar: boolean = false; get bar(): boolean { return this._bar; } set bar(value: boolean) { this._bar = value; } } That will produce this JavaScript, using the ECMAScript 5 Object.defineProperty() feature. var foo = (function () { function foo() { this._bar = false; … Read more