Modules(模块)
每一个ES6模块都是一个包含JS代码的文件,模块本质上就是一段脚本,而不是用 module 关键字定义一个模块。默认情况下模块都是在严格模式下运行。模块功能主要由两个命令构成:export和import。export命令用于用户自定义模块,规定对外接口;import命令用于输入其他模块提供的功能,同时创造命名空间(namespace),防止函数名冲突。
export
export用于从给定文件(或模块)导出函数和对象。
- export { name1, name2, …, nameN };
- export { variable1 as name1, variable2 as name2, …, nameN };
- export let name1, name2, …, nameN; // also var
- export let name1 = …, name2 = …, …, nameN; // also var, const
- export default expression;
- export default function (…) { … } // also class, function*
- export default function name1(…) { … } // also class, function*
- export { name1 as default, … };
- export * from …;
- export { name1, name2, …, nameN } from …;
- export { import1 as name1, import2 as name2, …, nameN } from …;
单个导出
- // export.js
- export let firstName = 'Michael';
- export let lastName = 'Jackson';
- export let year = 1958;
- function add(x, y) {
- return x + y;
- }
- export { add };
- export function multiply(x, y) {
- return x * y;
- };
批量导出
- // export.js
- let firstName = 'Michael';
- let lastName = 'Jackson';
- let year = 1958;
- function multiply(x, y) {
- return x * y;
- }
- export {firstName, lastName, year, multiply};
重命名导出
- let n = 1;
- function f()) {
- }
- export { n as m, f as g};
默认导出,每个模块只能有一个默认导出:
- // exportDefault.js
- function f() {
- }
- export default f;
- export{ f as default };
import
import用于从外部模块、其他脚本中导入函数、对象或者原型,这些被导入的模型必须在其他的模块或者脚本中被导出的。
- import defaultMember from "module-name";
- import * as name from "module-name";
- import { member } from "module-name";
- import { member as alias } from "module-name";
- import { member1 , member2 } from "module-name";
- import { member1 , member2 as alias2 , [...] } from "module-name";
- import defaultMember, { member [ , [...] ] } from "module-name";
- import defaultMember, * as name from "module-name";
- import "module-name";
无对象导入,如果模块包含一些逻辑要执行,且不会导出任何对象,此类对象也可以被导入到另一模块中。
- import './module';
导入默认对象,采用Default导出方式导出对象,该对象在import声明中将直接被分配给某个引用。
- import d from './exportDefault';
批量导入
- import {firstName, lastName, year, multiply} from './export';
重命名导入
- import { lastName as surname } from './export';
导入所有对象
- import * as o from './export';
import命令导入的对象可能是一个变量,也可能是一个函数,或者一个类,要视具体情况而定。import与require的差异较大,好不要混用。
实例
f10_modules_math.js
- export function sum(...x) {
- return x.reduce((m, n) => m + n);
- }
- export var pi = 3.141593;
f10_modules_app.js
- import * as math from "f10_modules_math";
- function execute() {
- console.log("π = " + math.sum(math.pi));
- console.log("2π = " + math.sum(math.pi, math.pi));
- console.log("3π = " + math.sum(math.pi, math.pi, math.pi));
- console.log("4π = " + math.sum(math.pi, math.pi, math.pi, math.pi));
- }
- export { execute };
f10_modules.js
- import * as app from "f10_modules_app";
- function f10_modules() {
- console.log("\nf10:Modules");
- app.execute(); // 输出:π = 3.141593 2π = 6.283186 3π = 9.424779 4π = 12.566372
- }
完整代码:
ES6.zip |