What are the three import methods in es6

Method: 1. Pack all the variables exported in a file into an object and import it with the "import * as from "module"" statement; 2. Use the "import name it as you like from "module"" statement ;3. Use the "import {specified name} from "module"" statement.

The operating environment of this tutorial: Windows 7 system, ECMAScript version 6, Dell G3 computer.

es6 import three import methods

import Name it arbitrarily from "module identifier"

This will only take effect if there is a default export export syntax in the module

// A.js
export default 20
// B.js
import A from './A'
上面的代码生效的前提是，只有在A.js中有默认导出的export default语法时才会生效。
这种不使用｛｝来引用模块的情况下，import模块的命名是随意的，即如下三种引用命名都是正确的：
//B.js
import A from './A'
import B from './A'
import Something from './A'
因为它总是会解析到A.js中默认的export default

import {specified name} from "module identifier"

It will only take effect if there is code in the module named export name with the specified name

//A.js
export const A = 21
//B.js
import { A } from './A'

代码生效的前提是，只有在模块A.js中有如下命名导出为A的export name的代码,
而且，在明确声明了命名导出后，那么在另一个js中使用{}引用模块时，import时的模块命名是有意义的，如下：
// B.js
import { A } from './A'                 // 正确，因为A.js中有命名为A的export
import { B } from './A'                 // 错误！因为A.js中没有命名为B的export

import * as from "module identifier" (packaged into an object )

Pack all the variables exported in a file into an object.
For example:

export const sqrt1 = Math.sqrt;
export const sqrt2= Math.sqrt;



import * as sqrtobj from "....."
sqrtobj.sqrt1
sqrtobj.sqrt2

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