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I'm building a Node.js app (Node v10.11.0) and want to do it in a OOP-way without using Typescript. So I've built some classes like this:

class Component {
  constructor(param1, param2, param3) {
    this.param1= param1;
    this.param2 = param2;
    this.param3 = param3;
  }
}

I wondered if there is a way in javascript to map the arguments of the constructor automatically without writing this.param1 = param1 for every single constructor argument.

I already tried running over arguments object with somthing like this:

constructor(param1, param2, param3) {
  Array.from(arguments).forEach(arg => {
    this[arg] = arg;
  }
}

but this doesn't work. The result of this approach is:

console.log(new Component("arg1", "arg3", "arg3"))

// Component { arg1: "arg1", arg2: "arg2", arg3: "arg3" }
// I want to have this:
// Component { param1: "arg1", param2: "arg2", param3: "arg3" }

I'm building a Node.js app (Node v10.11.0) and want to do it in a OOP-way without using Typescript. So I've built some classes like this:

class Component {
  constructor(param1, param2, param3) {
    this.param1= param1;
    this.param2 = param2;
    this.param3 = param3;
  }
}

I wondered if there is a way in javascript to map the arguments of the constructor automatically without writing this.param1 = param1 for every single constructor argument.

I already tried running over arguments object with somthing like this:

constructor(param1, param2, param3) {
  Array.from(arguments).forEach(arg => {
    this[arg] = arg;
  }
}

but this doesn't work. The result of this approach is:

console.log(new Component("arg1", "arg3", "arg3"))

// Component { arg1: "arg1", arg2: "arg2", arg3: "arg3" }
// I want to have this:
// Component { param1: "arg1", param2: "arg2", param3: "arg3" }

• javascript
• node.js
• class
• oop

Share Improve this question Follow asked Jan 14, 2020 at 12:35 Ma KobiMa Kobi 90477 silver badges2222 bronze badges 1

• There is nothing to be gained from this. It will not make any difference performance wise and it will make it way harder to read. – adiga Commented Jan 14, 2020 at 12:39

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2 Answers 2

Sorted by: Reset to default 12

If you want the constructor to accept discrete arguments, there's nothing much better than the individual assignment you're already doing, at least for now.

You could have the constructor accept an object instead, which would let you do this:

constructor(args) {
    Object.assign(this, args);
}

which you call like this:

new Component({param1: "arg1", param2: "arg2", param3: "arg3"});

but if it's just one to three parameters, that's creating extra work at every call site rather than once in the constructor code, and the constructor code is less clear.

A third option is to accept a rest parameter:

constructor(...args) {
    ["param1", "param2", "param3"].forEach((name, index) => {
        this[name] = args[index];
    });
}

which you call in the normal way, but again while it's subjective, to me readability is impaired.

---

Just as a side note, as I think you probably know, TypeScript has this feature. It's increasingly mon now to use TypeScript (which piles to JavaScript for use on browsers). TypeScript isn't tied to Angular, you can use it with just about any framework (or none).

In TypeScript, for instance:

// TypeScript
class Component {
    constructor(
        public param1: string,
        public param2: string,
        public param3: string
    ) {
    }
}

There's no code necessary in the constructor at all, TypeScript automatically assigns those parameter values to those public properties. (You can also use private or protected.)

Since you are passing an object as param, you can use the Object.keys

Sample snippet code

class Component {
  constructor(args) {
    Object.keys(args).forEach(argKey => this[argKey] = args[argKey])
  }
}

let a = new Component({param1: "arg1", param2: "arg2", param3: "arg3"})


console.log(a)

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