Closures

[java0219334930]

Hi,
I’m struggling to understand this bloke of code from the Eloquent JavaScript (2018) - Chapter 3.
Wondering if anyone could help me understand what is going on here?
Thanks!

function multiplier(factor) {
return number => number * factor;
}

let twice = multiplier(2);
console.log(twice(5));
// → 10

[mirja_t]

function multiplier(factor) { // factor (2) passed as argument by function invocation
	console.log(factor); // output: 2
	return number => number * factor; // function returned to let twice
}

let twice = multiplier(2); // returns a function: number => number * factor (passes 2 as factor)
console.log(multiplier(2)); // output: number => number * factor
console.log(twice(5)); // output 10

Edited after clarification by @mtf

[mtf]

@mirja_t

The parameter factor is a function

On the face of it, we can see that factor is a number.

The factory function then returns a function with that factor as a constant. In the example above, twice is the returned function with a constant set at 2. Any value we pass into that function will return double its value.

---

There are two kinds of factory functions, one that returns an object with supplied property values, and one that returns a function with a supplied constant, as above. The latter may sometimes be called a function factory.

[mirja_t]

Thank you for your clarification. I edited my previous post and hope it is clearer now.