Using spread operator multiple times in javascript?

Question

Why can\'t spread operator be used multiple times?

let arr = [[[1, 2, 3]]];

console.log(arr); // Array [ Array[1] ]
console.log(...arr); // Array [ Array[3]         


        

Answer 1

Because ...arr isn't like a function that returns a value in normal scenarios (you can test this by just typing ...[[1,2,3]] in console, if ... operated like a normal function we would expect a return of [1 2 3]. For that reason you can't chain spreads. From MDN:

The spread operator allows an expression to be expanded in places where multiple arguments (for function calls) or multiple elements (for array literals) are expected.

Ergo, spreads need to happen within array literals, object literals (if using obj spread, which is ES7) or within function calls So you could do console.log(...[].concat(...arr))