javascript变量名的意思是{花括号} [英] What do {curly braces} around javascript variable name mean

问题描述

编辑
在查看JSHint后，我发现这个'解构表达式'在ES6（使用esnext选项）或Mozilla JS扩展（使用moz）中可用和这个然而在阅读之后，我仍然不了解为什么使用

我在 MDN

  var ui = require（sdk / ui）; 
 var {ActionButton} = require（sdk / ui / button / action）; 
  

第二行的大括号是干什么用的？为什么在第一行没有花括号？

解决方案

这就是所谓的解构赋值，这是 JavaScript 1.7 （和

  var ActionButton = require（sdk / ui / button / action）。 
  

这个例子看起来很愚蠢，因为只有一个项目被分配。但是，您可以使用此模式一次分配多个变量：

  {x，y} = foo; 
  

相当于：

  x = foo.x;信息范讯卉范信辛
  

这也可以用于数组。例如，您可以轻松地交换两个值而不使用临时变量：

  var a = 1; 
 var b = 3; 
 
 [a，b] = [b，a]; 
  

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浏览器支持可以使用 kangax'ES6兼容性表格。

EDIT After looking at JSHint I found this 'destructuring expression' is available in ES6 (use esnext option) or Mozilla JS extensions (use moz) and this however after reading it I still don't understand why it is used

I have come across the following code on MDN

var ui = require("sdk/ui");
var { ActionButton } = require("sdk/ui/button/action");

What do the braces on the second line do and why are they used? Why are there no braces on the first line?

解决方案

This is what's known as a destructuring assignment, and it's a new feature of JavaScript 1.7 (and ECMAScript 6) (Currently, only available in the FireFox JavaScript engine.) Roughly, it would translate into this:

var ActionButton = require("sdk/ui/button/action").ActionButton;

It seems silly in this example, as there's only one item being assigned. However, you'd be able to use this pattern to assign multiple variables at once:

{x, y} = foo;

Is the equivalent to:

x = foo.x;
y = foo.y;

This can also be used for arrays. For example, you could easily swap two values without using a temporary variable:

var a = 1;
var b = 3;

[a, b] = [b, a];

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Browser support can be tracked using kangax' ES6 compatibility table.

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