CODEWITHSUNDEEP
javascriptclass
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Reputation: 841

Setting Class values in constructor to parameters

I have this code, which is kinda long winded but gets there in the end …

class WorksButLongWinded {
  constructor (callback, params = {}) {
    // defaults ...
    this.foo = "string";
    this.bar = 200;

    this.callback = callback;

    // params ...
    if( typeof params.foo != "undefined" ) { this.foo = params.foo }
    if( typeof params.bar != "undefined" ) { this.bar = params.bar }
  }
}

I thought I might try using destructuring to speed things along, like this:

class DoesNotWork {
  constructor (callback, params = {}) {
    {
      this.foo = "string", 
      this.bar = 200
    } = params;

    this.callback = callback;

  }
}

... except that doesn't work. It doesn't even pass syntax muster.

What is a clean and simple way of writing a class constructor that takes an optional params object with various optional parameters that override some default values?

Upvotes: 0

Views: 46

Answers (2)

Derek 朕會功夫
Derek 朕會功夫

Reputation: 94299

You mean something like this?

class WorksButLongWinded {
  constructor(callback, params) {
    let defaults = {
      foo: "string",
      bar: 200
    };

    this.callback = callback;
    Object.assign(this, defaults, params);
  }
}

let a = new WorksButLongWinded(() => {});
console.log(a.foo);  // "string"
console.log(a.bar);  // "200"

let b = new WorksButLongWinded(() => {}, {foo: "bar"});
console.log(b.foo);  // "bar"
console.log(b.bar);  // "200"

Object.assign does exactly what you want.

Upvotes: 2

Shubham Gupta
Shubham Gupta

Reputation: 2646

I think the way you are destructuring is incorrect. Try the below code where we destructure from params and then assign the values to this.

class WorksButLongWinded {
  constructor (callback, params = {}) {
    const {foo = "string", bar = 200} = params;
    this.foo = foo;
    this.bar = bar;
    this.callback = callback;
  }
}

Upvotes: 1

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