Aaron Aaron - 5 months ago 9
Javascript Question

Is it possible to destructure instance/member variables in a JavaScript constructor?

Is it possible to use destructuring assignment in a JavaScript class' constructor to assign the instance variables similar to how you can do it to normal variables?

The following example works:

var options = {one: 1, two: 2};
var {one, two} = options;
console.log(one) //=> 1
console.log(two) //=> 2


But I cannot get something like the following to work:

class Foo {
constructor(options) {
{this.one, this.two} = options;
// This doesn't parse correctly and wrapping in parentheses doesn't help
}
}

var foo = new Foo({one: 1, two: 2});
console.log(foo.one) //=> I want this to output 1
console.log(foo.two) //=> I want this to output 2

Answer

There are multiple ways of doing this. The first one uses destructuring only and assigns the properties of options to properties on this:

class Foo {
  constructor(options) {
    ({one: this.one, two: this.two} = options);
    // Do something else with the other options here
  }
}

The extra parentheses are needed, otherwise the JS engine might mistake the { ... } for an object literal or a block statement.

The second one uses Object.assign and destructuring:

class Foo {
  constructor(options) {
    const {one, two} = options;
    Object.assign(this, {one, two});
    // Do something else with the other options here
  }
}

If you want to apply all your options to the instance, you could use Object.assign without destructuring:

class Foo {
  constructor(options) {
    Object.assign(this, options);
  }
}
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