class Testone{
    constructor(value){
        Object.defineProperty(this, 'doSomething', {
            enumerable: false,
            configurable: false,
            writable: false,
            value: () => {
                //do whatever
            }
        });
    }
} 

const doWhatever = () => {
    //do whatever
} 

class Testtwo{
    constructor(value){
        Object.defineProperty(this, 'doSomething', {
            enumerable: false,
            configurable: false,
            writable: false,
            value: doWhatever
        });
    }
}

My thought is that Testtwo should be more efficient, since doWhatever would only exist in memory once then get pointed to by every instance of Testtwo. Testone would instantiate a new anonymous function for each new instance.

1. Does Testone actually create a new anonymous function each time? Is Testtwo therefor more efficient or is it also creating separate instances of doWhatever?

2. Am I missing some major caveat to one over the other (other than variable scope)?

My benchmarking consistently shows ~2% difference in instantiation time, with Testtwo indeed being faster... but that's not exactly confirmation.

CodePudding user response：

Yes. Testone create new doSomething function every time, but Testtwo uses existing one.

Proof:

class Testone{
    constructor(value){
        Object.defineProperty(this, 'doSomething', {
            enumerable: false,
            configurable: false,
            writable: false,
            value: () => {
                //do whatever
            }
        });
    }
} 

const doWhatever = () => {
    //do whatever
}

class Testtwo{
    constructor(value){
        Object.defineProperty(this, 'doSomething', {
            enumerable: false,
            configurable: false,
            writable: false,
            value: doWhatever
        });
    }
}

const f1 = new Testone()
const f2 = new Testone()
console.log('Testone', f1.doSomething === f2.doSomething)

const s1 = new Testtwo()
const s2 = new Testtwo()
console.log('Testtwo', s1.doSomething === s2.doSomething)