d.ts What is it

js File missing type ,ts So many types of data are gone , So you need a d.ts File to mark a js The type of objects in the library .

typings It's on the Internet d.ts database .

Simply speaking , Is to describe the member types in the library to give TS With .

benefits ： code safety , The editor can intelligently remind

There are many more definitions export Data type of , and interface For external modules to call . Obviously, it's the data specification .

Declaration file

When using third-party libraries , You need to reference its declaration file

$('#foo');
// or
jQuery('#foo');

Use declare Keyword to define its type , help TS Determine the incoming type ：

declare var jQuery: (selector: string) => any;

jQuery('#foo');

declare The defined type will only be used for compile time checks , The compilation result will be deleted .

Put the type declaration in a separate file , This is the declaration file .

// jQuery.d.ts

declare var jQuery: (string) => any;

Use /// Indicates that the declaration file is referenced ：

/// <reference path="./jQuery.d.ts" />

jQuery('#foo');

Index signature

Can be accessed by string js Objects in the , Save references to other objects .