CODEWITHSUNDEEP
javascript
Vladyslav Zavalykhatko
Vladyslav Zavalykhatko

Reputation: 17364

Fill object in Javascript with expected properties

I have a prototype

class Animal() {
    constructor(name, weight) {
        this.name = name
        this.weight = weight
    }
}

and some coming object, which contains these properties plus something else

const obj = {
    name: "name",
    weight: 5,
    someRedundantProp: "bla"
}

I really enjoy JS mapping with Object.assign which would generically create an object for me with all properties, but here I want to fill this new object only with essential fields. Surely, I can map this object like

new Animal(obj.name, obj.weight)

but if at some point I would introduce new properties I will have to change code here, what I don't want to.

Is there some better way?

Upvotes: 2

Views: 4620

Answers (3)

steliosbl
steliosbl

Reputation: 8921

This should work for you:

class Animal {
    constructor(obj) {
        const defaultFields = {
            name: "",
            weight: 0
        }
        Object.keys(defaultFields).forEach(key => defaultFields[key] = obj[key]);
        Object.assign(this, defaultFields);
    }
}

Upvotes: 1

lumio
lumio

Reputation: 7575

You could check if the first argument is an object and then assign the object to this.

But be warned, this has some nasty side effects too.

class Animal {
  constructor( obj ) {
    // Create an object that holds all available options
    const defaultOptions = {
      name: '',
      weight: 0,
    };
    
    // Go over all available options
    Object.keys( defaultOptions ).forEach( key => {
      // Check if obj has key, otherwise use default option
      this[ key ] = obj[ key ] || defaultOptions[ key ];
    } );
  }
}

const obj = {
  name: "name",
  weight: 5,
  someRedundantProp: "bla"
}

const a = new Animal( obj );
console.log( a );

Upvotes: 1

Vladyslav Zavalykhatko
Vladyslav Zavalykhatko

Reputation: 17364

I came to this solution for now

let animal = new Animal()
Object.keys(animal).forEach(field => animal[field] = obj[field])

Upvotes: 0

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