Is it possible to define a dynamically named property using object literal in JavaScript?

问题

Consider the following

var a = {foo: "bar"};

Equivalent to

var a = {};
a.foo = "bar";

Equivalent to

var a = {};
a['foo'] = "bar";

Equivalent to

var a = {}
var b = "foo";
a[b] = "bar";

Is it possible to do something like

var b = "foo";
var a = { [b]: "bar" };

Such that the result would be

// => {foo: "bar"}

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Acceptable solutions are in JavaScript or CoffeeScript

回答1:

No.

There is no way to do it using object literal notation.

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UPDATE: According to the ECMAScript standard 6.0 you are now able to do the following:

var b = 'foo';
var a = { [b]: 'bar' };

console.log( a.foo );  // "bar"

However, this solution won't work in old browsers, which do not support ES6.

回答2:

ES6 supports computed properties.

// code from my original question now works in ES6 !
let b = "foo";
let a = { [b]: "bar" };

a.foo; //=> "bar"

Any expression can be used within the [] to define the property name

let a = {
  [(xs => xs.join(''))(['f','o','o'])]: 'bar'
};

a.foo; //=> "bar"

If you need to rely on this behavior in an ES5 world, you can lean on the very capable babel.js to transpile your ES6 code to ES5-compatible code.

回答3:

JSON parse allows you to convert a JSON string into an object:

JSON.parse('{"'+dynamicProperty+'":"bar"}');

This is not exactly an object litteral, but if your objective is to enter your property name as a variable it works.

回答4:

As others have said, no, there's currently no syntax for interpolated key strings in object literals in CoffeeScript; but it seems at some point this feature existed! In these GitHub issues there's some discussion about it: #786 and #1731.

It's implemented in Coco and LiveScript as:

b = 'foo'
a = {"#{b}": 'baz'}

# Or..
a = {(b): 'bar'}

回答5:

As of CoffeeScript version 1.9.1 this works:

b = "foo"
a = "#{b}": "bar"

It compiles to:

var a, b, obj;

b = "foo";

a = (
  obj = {},
  obj["" + b] = "bar",
  obj
);

Try it.

回答6:

JavaScript

var a, b;
(a = {})[b = 'foo'] = 'bar';

CoffeeScript

(a = {})[b = 'foo'] = 'bar'

回答7:

To answer your question, this is the only way that I know of. It uses eval. But beware, eval is evil!

var b = "foo";
var a = eval('({ ' + b + ': ' + '"bar"' + ' })');

This is an ugly solution. To play it safe you should not rely on this. Don't use it!

来源：https://stackoverflow.com/questions/13997748/is-it-possible-to-define-a-dynamically-named-property-using-object-literal-in-ja