Built in objects for typescript

JavaScript There are many built-in objects in , They can be directly in TypeScript As a defined type .

The built-in object refers to the object in the global scope according to the standard （Global） Objects that exist on . The standard here refers to ECMAScript And other environments （ such as DOM） Standards for .

ECMAScript Built in objects for

ECMAScript The built-in objects provided by the standard are ：

Boolean、Error、Date、RegExp etc. .

We can do it in TypeScript Define variables as these types ：

let b: Boolean = new Boolean(1);
let e: Error = new Error('Error occurred');
let d: Date = new Date();
let r: RegExp = /[a-z]/l

More built-in objects , You can see MDN Documents .

And their definition file , It's in TypeScript In the definition file of the core library .

DOM and BOM Built in objects for

DOM and BOM The built-in objects provided are ：

Document、HTMLElement、Event、NodeList etc. .

TypeScript These types are often used in ：

let body: HTMLElement = document.body;
let allDiv: NodeList = document.querySelectorAll('div');
document.addEventListener('click', funciton(e: MouseEvent) {
    
  // ...
});

Their definition files are also in TypeScript In the definition file of the core library .

TypeScript Definition file of core library

TypeScript The definition file of the core library defines the types required by all browser environments , And it is preset in TypeScript Medium .

When you are using some common methods ,TypeScript In fact, I've done a lot of types of judgment for you , such as ：

Math.pow(10, '2'); // error TS2345: Argument of type 'string' is not assignable to parameter of type 'number'.

In the example above ,Math.pow Must accept two number Parameters of type . in fact Math.pow The types of are defined as follows ：

interface Math {
    
  /** * Returns the value of a base expression taken to a specified power. * @param x The base value of the expression. * @param y The exponent value of the expression. */
  pow(x: number, y: number): number;
}

For another DOM Examples in ：

document.addEventListener('clicl', function(e) {
    
  console.log(e.targetCurrent); // error TS2339: Property 'targetCurrent' does not exist on type 'MouseEvent'.
});

In the example above ,addEventListener The method is in TypeScript Defined in the core library ：

interface Document extends Node, GlobalEventHandlers, NodeSelector, DocumentEvent {
    
  addEventListener(type: string, listener: (ev: MouseEvent) => any, useCapture?: boolean): void;
}

therefore e To be inferred as MouseEvent, and MouseEvent It's not targetCurrent Attribute , That's why I made a mistake .

use TypeScript Write Node.js

Be careful ,TypeScript The definition of the core library does not contain Node.js part .

Node.js Not part of the built-in object , If you want to use TypeScript Write Node.js, A third-party declaration file needs to be introduced ：

npm install @types/node --save-dev

Extract from ：《TypeScript Introductory tutorial 》