Array.from() vs spread syntax

Is there some difference between using Array.from(document.querySelectorAll('div')) or [...document.querySelectorAll('div')]?

Here is a example:

let spreadDivArray = [...document.querySelectorAll('div')];
console.log(spreadDivArray);

let divArrayFrom = Array.from(document.querySelectorAll('div'));
console.log(divArrayFrom);

The console.log() will log the same result.

Is there any performance difference?

Spread element (it's not an operator) works only with objects that are iterable (i.e. implement the @@iterator method). Array.from() works also on array-like objects (i.e. objects that have the length property and indexed elements) which are not iterable. See this example:

const arrayLikeObject = { 0: 'a', 1: 'b', length: 2 };

// This logs ['a', 'b']
console.log(Array.from(arrayLikeObject));
// This throws TypeError: arrayLikeObject[Symbol.iterator] is not a function
console.log([...arrayLikeObject]);

Also, if you just want to convert something to array, I think it's better to use Array.from() because it's more readable. Spread elements are useful for example when you want to concatenate multiple arrays (['a', 'b', ...someArray, ...someOtherArray]).

Well, Array.from is a static method, i.e., a function whereas the spread syntax is part of the array literal syntax. You can pass functions around like data, you can invoke them once, several times or not at all. This isn't possible with the spread syntax, which is static in this regard.

Another difference, which @nils has already pointed out, is that Array.from also works with array-like objects, which don't implement the iterable protocol. spread on the other hand requires iterables.

The difference is that spread allows an array to be expanded. Whereas from() creates a new array. .from() doesn't expand upon anything, it creates a new array based on the data provided; the spread operator on the other hand can expand an array with new properties.

If the input is iterable they do the exact same thing.

However, based on the benchmarks, the spread operator seems to perform better for a Set.

https://jsben.ch/5lKjg

let set = new Set();
for (let i = 0; i < 10000; i++) {
  set.add(Math.random());
}


let tArrayFrom = window.performance.now()

let arr = Array.from(set)

console.log("Array.from():", window.performance.now() - tArrayFrom + "ms")


// slightly faster in most of the runs:
let tSpread = window.performance.now()

let arr2 = [...set];

console.log("Spread syntax:", window.performance.now() - tSpread + "ms")