Javascript Array formatting

Question

I am new to javascript, recently I am studying javascript array and object.

if I have a object

const initialValue = {
 a: 30,
 b: 40,
 c: 50
}
const initialValueKey = Object.keys(initialValue)
const [, , , ...value] = initialValueKey;

I wonder what is this [, , , ...value] expression, I know ...is spread operator, but i'm not sure what the value of [, , , ...value] here.

• Phil: It's skipping the first 3 values and assigning the rest of the array to value. Try making your initialValue with more properties to see the difference
• Thomas: it's a complicated way to write const value = initialValueKey.slice(3);

Answer 1

It is a way to retrieve "other values", or retrieving the values and skipping the first n.

Here's an example:

const obj = {
 a: 1,
 b: 2,
 c: 3,
 d: 4,
 e: 5
};
const data = Object.keys(obj);
const [,,, ...values] = data;
console.log(values);

Answer 2

This is a way to assign the variables to arrays. the two commas in this example skipsthe first 2 elements

const initialValue = {
 a: 30,
 b: 40,
 c: 50,
 d: 70
}
const initialValueKey = Object.keys(initialValue)
const [, , ...value] = initialValueKey;
console.log(value);