- Angular UI Development with PrimeNG
- Sudheer Jonna Oleg Varaksin
- 290字
- 2021-07-15 17:32:55
Modules
ECMAScript 2015 has introduced built-in modules. The features of modules are as follows:
- Each module is defined in its own file.
- Functions or variables defined in a module are not visible outside unless you explicitly export them.
- You can place the export keyword in front of any variable, function, or class declaration to export it from the module.
- You can use the import keyword to consume the exported variable, function, or class declaration.
- Modules are singletons. Only a single instance of a module exists, even if it was imported multiple times.
Some exporting possibilities are listed here:
// export data
export let color: string = "red";
// export function
export function sum(num1: number, num2: number) {
return num1 + num1;
}
// export class
export class Rectangle {
constructor(private length: number, private width: number) { }
}
You can declare a variable, function, or class and export it later. You can also use the as keyword to rename exports. A new name is the name used for importing:
class Rectangle {
constructor(private height: number, private width: number) { }
}
export {Rectangle as rect};
Once you have a module with exports, you can access its functionality in another module using the import keyword:
import {sum} from "./lib.js";
import {Rect, Circle} from "./lib.js";
let sum = sum(1, 2);
let rect = new Rect(10, 20);
There is a special case that allows you to import the entire module as a single object. All exported variables, functions, and classes are available on that object as properties:
import * as lib from "./lib.js";
let sum = lib.sum(1, 2);
Imports can be renamed with the as keyword and used under the new name:
import {sum as add} from "./lib.js";
let sum = add(1, 2);
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