如何在 ES6中解构为动态命名的变量？

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最佳答案

Short answer: it's impossible and it won't be possible.

Reasoning behind this: it would introduce new dynamically named variables into block scope, effectively being dynamic eval, thus disabling any performance optimization. Dynamic eval that can modify scope in fly was always regarded as extremely dangerous and was removed from ES5 strict mode.

Moreover, it would be a code smell - referencing undefined variables throws ReferenceError, so you would need more boilerplate code to safely handle such dynamic scope.

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It's not impossible to destructure with a dynamic key. To prevent the problem of creating dynamic variables (as Ginden mentioned) you need to provide aliases.

const user = {
id: 42,
displayName: "jdoe",
fullName: {
firstName: "John",
lastName: "Doe"
}
};


const fields = [ 'id', 'fullName' ];
const object = {};


const {[fields[0]]: id, [fields[1]]: fullName} = user;


console.log(id); // 42
console.log(fullName); // { firstName: "John", lastName: "Doe" }

To get around the problem of having to define static aliases for dynamic values, you can assign to an object's dynamic properties. In this simple example, this is the same as reverting the whole destructuring, though :)

const user = {
id: 42,
displayName: "jdoe",
fullName: {
firstName: "John",
lastName: "Doe"
}
};


const fields = [ 'id', 'fullName' ];
const object = {};


({[fields[0]]: object[fields[0]], [fields[1]]: object[fields[1]]} = user);


console.log(object.id); // 42
console.log(object.fullName); // { firstName: "John", lastName: "Doe" }

sources:

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As discussed before, you can't destruct into dynamically named variables in JavaScript without using eval.

But you can get a subset of the object dynamically, using reduce function as follows:

const destruct = (obj, ...keys) =>
keys.reduce((a, c) => ({ ...a, [c]: obj[c] }), {});


const object = {
color: 'red',
size: 'big',
amount: 10,
};


const subset1 = destruct(object, 'color');
const subset2 = destruct(object, 'color', 'amount', 'size');
console.log(subset1);
console.log(subset2);

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You can't destruct without knowing the name of the keys or using an alias for named variables

// you know the name of the keys
const { id, fullName } = user;


// use an alias for named variables
const { [fields[0]]: id, [fields[1]]: fullName } = user;

A solution is to use Array.reduce() to create an object with the dynamic keys like this:

const user = {
id: 42,
displayName: "jdoe",
fullName: {
firstName: "John",
lastName: "Doe"
}
};


const fields = [ 'id', 'fullName', 'age' ];


const obj = fields.reduce((acc, k) => ({ ...acc, ...(user.hasOwnProperty(k) && { [k]: user[k] }) }), {});


for(let k in obj) {
console.log(k, obj[k]);
}

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Paul Kögel's answer is great, but I wanted to give a simpler example for when you need only the value of a dynamic field but don't need to assign it to a dynamic key.

let obj = {x: 3, y: 6};
let dynamicField = 'x';


let {[dynamicField]: value} = obj;


console.log(value);

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I believe that the above answers are intellectual and valid because all are given by pro developers. :). But, I have found a small and effective solution to destructure any objects dynamically. you can destructure them in two ways. But both ways are has done the same action. Ex:

const user = {
id: 42,
displayName: "jdoe",
fullName: {
firstName: "John",
lastName: "Doe"
}
};

using "Object.key", "forEach" and "window" object.

Object.keys(user).forEach(l=>window[l]=user[l]);

Simply using Object. assign method.
```
Object.assign(window, user)
```

Output:

console.log(id, displayName, fullName)
// 42 jdoe {firstName: "John", lastName: "Doe"}

Anyway, I am a newbie in JS. So, don't take it as an offense if you found any misleading info in my answer.