Array map function doesn't change elements

Question

In JavaScript, I have an array, which is

array = [true, false]

In some cases, I am trying to initialize this array

array.map(item => {
   item = false
})

After running the above code, the array is not changed, it is still [true, false], so is .map not reliable sometimes?

---

ONE MORE QUESTION: After running my below code, the array is changed. Why does it work in this case?

let array = [{id:1, checked: false}, {id:2, checked:true}]
array.map(item => {
    item.checked = true
})

array becomes [{id:1, checked: true}, {id:2, checked:true}]

Benjy

.map function doesn't change original array, it returns another array which you should use. – Crispa

Answer 1

JavaScript Array map() Method

*)creates a new array with the results of calling a function for every array element and it calls the provided function once for each element in an array, in order.

Note: map() Method does not execute the function for array elements without values and it does not change the original array.

more details

Polyp

Answer 2

Array map function is working fine. The map() method creates a new array with the results of calling a provided function on every element in this array. map() does not mutate the array on which it is called.

var array = [true, false]



var new_array = array.map(function(item) {
  return false;
});

console.log(array)
console.log(new_array)

Nne

Answer 3

If your mapping is simple, you can do:

var array = [true, false];
array = array.map(_ => false);

console.log(array);
// [false, false]

Scotty

Using an underscore as a variable name is sometimes used when you're not actually going to use the variable for anything. It's purely a style-thing. – Scotty

Answer 4

.map() method is not mutable, check out its return value:

var arr2 = array.map(item => false)
console.log(arr2)

In functional programming, it's recommended that values do not change often, and JavaScript borrowed it. At least for .map() and .reduce() this is true. Make sure you know .map() well.

Halation