How to replace item in array?

Each item of this array is some number:

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

How to replace some item with a new one?

For example, we want to replace 3452 with 1010, how would we do this?

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
}

The Array.indexOf() method will replace the first instance. To get every instance use Array.map():

a = a.map(function(item) { return item == 3452 ? 1010 : item; });

Of course, that creates a new array. If you want to do it in place, use Array.forEach():

a.forEach(function(item, i) { if (item == 3452) a[i] = 1010; });

My suggested solution would be:

items.splice(1, 1, 1010);

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

Answer from @gilly3 is great.

Replace object in an array, keeping the array order unchanged

I prefer the following way to update the new updated record into my array of records when I get data from the server. It keeps the order intact and quite straight forward one liner.

users = users.map(u => u.id !== editedUser.id ? u : editedUser);

var users = [
{id: 1, firstname: 'John', lastname: 'Ken'},
{id: 2, firstname: 'Robin', lastname: 'Hood'},
{id: 3, firstname: 'William', lastname: 'Cook'}
];

var editedUser = {id: 2, firstname: 'Michael', lastname: 'Angelo'};

users = users.map(u => u.id !== editedUser.id ? u : editedUser);

console.log('users -> ', users);

Use indexOf to find an element.

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

Easily accomplished with a for loop.

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

First method

Best way in just one line to replace or update item of array

array.splice(array.indexOf(valueToReplace), 1, newValue)

Eg:

let items = ['JS', 'PHP', 'RUBY'];

let replacedItem = items.splice(items.indexOf('RUBY'), 1, 'PYTHON')

console.log(replacedItem) //['RUBY']
console.log(items) //['JS', 'PHP', 'PYTHON']

Second method

An other simple way to do the same operation is :

items[items.indexOf(oldValue)] = newValue

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'

You can edit any number of the list using indexes

for example :

items[0] = 5;
items[5] = 100;

ES6 way:

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

We wanna replace 3452 with 1010, solution:

const newItems = items.map(item => item === 3452 ? 1010 : item);

Surely, the question is for many years ago and for now I just prefer to use immutable solution, definitely, it is awesome for ReactJS.

For frequent usage I offer below function:

const itemReplacer = (array, oldItem, newItem) =>
  array.map(item => item === oldItem ? newItem : item);

A functional approach to replacing an element of an array in javascript:

const replace = (array, index, ...items) => [...array.slice(0, index), ...items, ...array.slice(index + 1)];

The immutable way to replace the element in the list using ES6 spread operators and .slice method.

const arr = ['fir', 'next', 'third'], item = 'next'

const nextArr = [
  ...arr.slice(0, arr.indexOf(item)), 
  'second',
  ...arr.slice(arr.indexOf(item) + 1)
]

Verify that works

console.log(arr)     // [ 'fir', 'next', 'third' ]
console.log(nextArr) // ['fir', 'second', 'third']

Replacement can be done in one line:

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

items[items.map((e, i) => [i, e]).filter(e => e[1] == 3452)[0][0]] = 1010

console.log(items);

Or create a function to reuse:

Array.prototype.replace = function(t, v) {
    if (this.indexOf(t)!= -1)
        this[this.map((e, i) => [i, e]).filter(e => e[1] == t)[0][0]] = v;
  };

//Check
var items = Array(523, 3452, 334, 31, 5346);
items.replace(3452, 1010);
console.log(items);

The easiest way is to use some libraries like underscorejs and map method.

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

_.map(items, function(num) {
  return (num == 3452) ? 1010 : num; 
});
=> [523, 1010, 334, 31, ...5346]

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

Well if anyone is interresting on how to replace an object from its index in an array, here's a solution.

Find the index of the object by its id:

const index = items.map(item => item.id).indexOf(objectId)

Replace the object using Object.assign() method:

Object.assign(items[index], newValue)

If you want a simple sugar sintax oneliner you can just:

(elements = elements.filter(element => element.id !== updatedElement.id)).push(updatedElement);

Like:

let elements = [ { id: 1, name: 'element one' }, { id: 2, name: 'element two'} ];
const updatedElement = { id: 1, name: 'updated element one' };

If you don't have id you could stringify the element like:

(elements = elements.filter(element => JSON.stringify(element) !== JSON.stringify(updatedElement))).push(updatedElement);

 items[items.indexOf(3452)] = 1010

great for simple swaps. try the snippet below

const items = Array(523, 3452, 334, 31, 5346);
console.log(items)

items[items.indexOf(3452)] = 1010
console.log(items)

Here is the basic answer made into a reusable function:

function arrayFindReplace(array, findValue, replaceValue){
    while(array.indexOf(findValue) !== -1){
        let index = array.indexOf(findValue);
        array[index] = replaceValue;
    }
}

var index = Array.indexOf(Array value);
        if (index > -1) {
          Array.splice(index, 1);
        }

from here you can delete a particular value from array and based on the same index you can insert value in array .

 Array.splice(index, 0, Array value);

Here's a one liner. It assumes the item will be in the array.

var items = [523, 3452, 334, 31, 5346] var replace = (arr, oldVal, newVal) => (arr[arr.indexOf(oldVal)] = newVal, arr) console.log(replace(items, 3452, 1010))

First, rewrite your array like this:

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

Next, access the element in the array through its index number. The formula to determine the index number is: n-1

To replace the first item (n=1) in the array, write:

items[0] = Enter Your New Number;

In your example, the number 3452 is in the second position (n=2). So the formula to determine the index number is 2-1 = 1. So write the following code to replace 3452 with 1010:

items[1] = 1010;

I solved this problem using for loops and iterating through the original array and adding the positions of the matching arreas to another array and then looping through that array and changing it in the original array then return it, I used and arrow function but a regular function would work too.

var replace = (arr, replaceThis, WithThis) => {
    if (!Array.isArray(arr)) throw new RangeError("Error");
    var itemSpots = [];
    for (var i = 0; i < arr.length; i++) {
	    if (arr[i] == replaceThis) itemSpots.push(i);
    }
    
    for (var i = 0; i < itemSpots.length; i++) {
	    arr[itemSpots[i]] = WithThis;
    }
    
    return arr;
};

presentPrompt(id,productqty) {
    let alert = this.forgotCtrl.create({
      title: 'Test',
      inputs: [
        {
          name: 'pickqty',
          placeholder: 'pick quantity'
        },
        {
          name: 'state',
          value: 'verified',
          disabled:true,
          placeholder: 'state',
          
        }
      ],
      buttons: [
        {
          text: 'Ok',
          role: 'cancel',
          handler: data => {

            console.log('dataaaaname',data.pickqty);
            console.log('dataaaapwd',data.state);
            

          for (var i = 0; i < this.cottonLists.length; i++){

            if (this.cottonLists[i].id == id){
                this.cottonLists[i].real_stock = data.pickqty;
             
            }
          }

          for (var i = 0; i < this.cottonLists.length; i++){

            if (this.cottonLists[i].id == id){
              this.cottonLists[i].state = 'verified';   
            
          }
        }
            //Log object to console again.
            console.log("After update: ", this.cottonLists)
            console.log('Ok clicked');
          }
        },
        
      ]
    });
    alert.present();
  }

As per your requirement you can change fields and array names.
thats all. Enjoy your coding.

The easiest way is this.

var items = Array(523,3452,334,31, 5346);
var replaceWhat = 3452, replaceWith = 1010;
if ( ( i = items.indexOf(replaceWhat) ) >=0 ) items.splice(i, 1, replaceWith);

console.log(items);
>>> (5) [523, 1010, 334, 31, 5346]

When your array have many old item to replace new item, you can use this way:

function replaceArray(array, oldItem, newItem) {
    for (let i = 0; i < array.length; i++) {
        const index = array.indexOf(oldItem);
        if (~index) {
            array[index] = newItem;
        }
    }
    return array
}

console.log(replaceArray([1, 2, 3, 2, 2, 8, 1, 9], 2, 5));
console.log(replaceArray([1, 2, 3, 2, 2, 8, 1, 9], 2, "Hi"));

const items = Array(1, 2, 3, 4, 5);
console.log(items)

items[items.indexOf(2)] = 1010
console.log(items)

This will do the job

Array.prototype.replace = function(a, b) {
    return this.map(item => item == a ? b : item)
}

Usage:

let items = ['hi', 'hi', 'hello', 'hi', 'hello', 'hello', 'hi']
console.log(items.replace('hello', 'hi'))

Output:

['hi', 'hi', 'hi', 'hi', 'hi', 'hi', 'hi']

The nice thing is, that EVERY array will have .replace() property.