How to replace an item in an array with JavaScript?

Question

Each item of this array is some number.

var items = Array(523,3452,334,31, ...5346);

How do I replace some number in with array with a new on

Answer 1

Easily accomplished with a for loop.

for (var i = 0; i < items.length; i++)
    if (items[i] == 3452)
        items[i] = 1010;

Answer 2

var index = items.indexOf(3452);

if (index !== -1) {
    items[index] = 1010;
}

Also it is recommend you not use the constructor method to initialize your arrays. Instead, use the literal syntax:

var items = [523, 3452, 334, 31, 5346];

You can also use the ~ operator if you are into terse JavaScript and want to shorten the -1 comparison:

var index = items.indexOf(3452);

if (~index) {
    items[index] = 1010;
}

Sometimes I even like to write a contains function to abstract this check and make it easier to understand what's going on. What's awesome is this works on arrays and strings both:

var contains = function (haystack, needle) {
    return !!~haystack.indexOf(needle);
};

// can be used like so now:
if (contains(items, 3452)) {
    // do something else...
}

Starting with ES6/ES2015 for strings, and proposed for ES2016 for arrays, you can more easily determine if a source contains another value:

if (haystack.includes(needle)) {
    // do your thing
}

Answer 3

If using a complex object (or even a simple one) and you can use es6, Array.prototype.findIndex is a good one. For the OP's array, they could do,

const index = items.findIndex(x => x === 3452)
items[index] = 1010

For more complex objects, this really shines. For example,

const index = 
    items.findIndex(
       x => x.jerseyNumber === 9 && x.school === 'Ohio State'
    )

items[index].lastName = 'Utah'
items[index].firstName = 'Johnny'

Answer 4

Use indexOf to find an element.

var i = items.indexOf(3452);
items[i] = 1010;

Answer 5

My suggested solution would be:

items.splice(1, 1, 1010);

The splice operation will remove 1 item, starting at position 1 in the array (i.e. 3452), and will replace it with the new item 1010.

Answer 6

var items = Array(523,3452,334,31,5346);

If you know the value then use,

items[items.indexOf(334)] = 1010;

If you want to know that value is present or not, then use,

var point = items.indexOf(334);

if (point !== -1) {
    items[point] = 1010;
}

If you know the place (position) then directly use,

items[--position] = 1010;

If you want replace few elements, and you know only starting position only means,

items.splice(2, 1, 1010, 1220);

for more about .splice