方括号 Javascript 对象键
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Square Brackets Javascript Object Key
提问by lcharbon
Can anyone explain how the why/how the below method of assigning keys in javascript works?
任何人都可以解释为什么/如何在javascript中分配键的以下方法是如何工作的？
a = "b"
c = {[a]: "d"}
return:
返回：
Object {b: "d"}
回答by Sean Vieira
It's the new ES2015 (the EcmaScript spec formally known as ES6) computed property name syntax. It's a shorthand for the someObject[someKey]assignment that you know from ES3/5:
它是新的 ES2015（正式称为 ES6 的 EcmaScript 规范）计算属性名称语法。这someObject[someKey]是您在 ES3/5 中知道的作业的简写：
var a = "b"
var c = {[a]: "d"}
is syntactic sugar for:
是语法糖：
var a = "b"
var c = {}
c[a] = "d"
回答by hygull
Really the use of []gives an excellent way to use actual value of variable as key/propertywhile creating JavaScript objects.
确实，使用[]提供了一种极好的方法，可以在创建 JavaScript对象时使用变量的实际值作为关键/属性。
I'm pretty much statisfied with the above answer and I appreciate it as it allowed me to write this with a little example.
I've executed the code line by line on Node REPL(Node shell).
我对上面的答案非常满意，我很感激，因为它让我可以用一个小例子来写这个。
我已经在Node REPL（Node shell）上逐行执行了代码。
> var key = "fullName"; // Assignment
undefined
>
> var obj = {key: "Rishikesh Agrawani"} // Here key's value will not be used
undefined
> obj // Inappropriate, which we don't want
{ key: 'Rishikesh Agrawani' }
>
> // Let's fix
undefined
> var obj2 = {[key]: "Rishikesh Agrawani"}
undefined
> obj2
{ fullName: 'Rishikesh Agrawani' }
>
回答by monireh d
const animalSounds = {cat: 'meow', dog: 'bark'};
const animal = 'lion';
const sound = 'roar';
{...animalSounds, [animal]: sound};
The result will be
结果将是
{cat: 'meow', dog: 'bark', lion: 'roar'};
回答by Eldiyar Talantbek
Also, only condition to use []notation for accessing or assigning stuff in objects when we don't yet know what it's going to be until evaluation or runtime.
此外，只有[]在评估或运行时我们还不知道它将是什么时，才可以使用符号来访问或分配对象中的内容。
