How to find the array index with a value?

Question

Say I've got this

imageList = [100,200,300,400,500];

Which gives me

[0]100 [1]200 etc.

Is there any way in JavaScript to return the index with the value?

I.e. I want the index for 200, I get returned 1.

• Manse: Excellent answer here -> stackoverflow.com/questions/237104/…
• Matt Ball: developer.mozilla.org/en/JavaScript/Reference/Global_Objects/…

Answer 1

You can use indexOf:

var imageList = [100,200,300,400,500];
var index = imageList.indexOf(200); // 1

You will get -1 if it cannot find a value in the array.

• voigtan: you can use developer.mozilla.org/en/JavaScript/Reference/Global_Objects/… or any Javascript framework to fix that.
• joedborg: Have just found it won't work in IE8. What's my alternative?
• joedborg: @voigtan How do I add this to my JS?
• joedborg: I've done it, thanks. IE will one day catch up with modern times!
• pelms: Also won't work in recent IE if in compatibility mode

Answer 2

For objects array use map with indexOf:

var imageList = [
 {value: 100},
 {value: 200},
 {value: 300},
 {value: 400},
 {value: 500}
];
var index = imageList.map(function (img) { return img.value; }).indexOf(200);
console.log(index);

---

In modern browsers you can use findIndex:

var imageList = [
 {value: 100},
 {value: 200},
 {value: 300},
 {value: 400},
 {value: 500}
];
var index = imageList.findIndex(img => img.value === 200);
console.log(index);

Its part of ES6 and supported by Chrome, FF, Safari and Edge

• Bindrid: Note that findIndex is not implemented in IE 11
• Jaqen H'ghar: @Bindrid it is written in the answer see "Its part of ES6 and supported by Chrome, FF, Safari and (Unfortunately only) IE edge"

Answer 3

Use jQuery's function jQuery.inArray

jQuery.inArray( value, array [, fromIndex ] )
(or) $.inArray( value, array [, fromIndex ] )

• James Blackburn: Was going to use the code marked as the correct answer but it seems that that code wont work in all versions of IE. This answer works in all versions of IE but I changed the code slightly: var arrayPosition = $.inArray( value, Array ); works perfectly
• Andrew: jQuery ≠ Javascript

Answer 4

Here is an another way find value index in complex array in javascript. Hope help somebody indeed. Let us assume we have a JavaScript array as following,

var studentsArray =
 [
 {
 "rollnumber": 1,
 "name": "dj",
 "subject": "physics"
 },
 {
 "rollnumber": 2,
 "name": "tanmay",
 "subject": "biology"
 },
 {
 "rollnumber": 3,
 "name": "amit",
 "subject": "chemistry"
 },
 ];

Now if we have a requirement to select a particular object in the array. Let us assume that we want to find index of student with name Tanmay.

We can do that by iterating through the array and comparing value at the given key.

function functiontofindIndexByKeyValue(arraytosearch, key, valuetosearch) {
 for (var i = 0; i < arraytosearch.length; i++) {
 if (arraytosearch[i][key] == valuetosearch) {
 return i;
 }
 }
 return null;
 }

You can use the function to find index of a particular element as below,

var index = functiontofindIndexByKeyValue(studentsArray, "name", "tanmay");
alert(index);

Answer 5

Use indexOf

imageList.indexOf(200)

Answer 6

how about indexOf ?

alert(imageList.indexOf(200));

Answer 7

Array.indexOf doesnt work in some versions of internet explorer - there are lots of alternative ways of doing it though ... see this question / answer : How do I check if an array includes an object in JavaScript?

• Simon_Weaver: according to this page developer.mozilla.org/en-US/docs/JavaScript/Reference/… you need Internet Explorer 9 for this feature (I almost wrongly assumed we were just talking IE 6 here)
• Manse: @Simon_Weaver on that page you linked there is a polyfill for all browsers using JavaScript 1.6 and up

Answer 8

When the lists aren't extremely long, this is the best way I know:

function getIndex(val) {
 for (var i = 0; i < imageList.length; i++) {
 if (imageList[i] === val) {
 return i;
 }
 }
}
var imageList = [100, 200, 300, 400, 500];
var index = getIndex(200);

Answer 9

It is possible to use a ES6 function Array.prototype.findIndex.

MDN says:

The findIndex() method returns the index of the first element in the array that satisfies the provided testing function. Otherwise -1 is returned.

var fooArray = [5, 10, 15, 20, 25];
console.log(fooArray.findIndex(num=> { return num > 5; }));
// expected output: 1

Find an index by object property.

To find an index by object property:

yourArray.findIndex(obj => obj['propertyName'] === yourValue)

For example, there is a such array:

let someArray = [
 { property: 'OutDate' },
 { property: 'BeginDate'},
 { property: 'CarNumber' },
 { property: 'FirstName'}
];

Then, code to find an index of necessary property looks like that:

let carIndex = someArray.findIndex( filterCarObj=> 
 filterCarObj['property'] === 'CarNumber');

Answer 10

In a multidimensional array.

---

Reference array:

var array = [
 { ID: '100' },
 { ID: '200' },
 { ID: '300' },
 { ID: '400' },
 { ID: '500' }
];

Using filter and indexOf:

var index = array.indexOf(array.filter(function(item) { return item.ID == '200' })[0]);

Looping through each item in the array using indexOf:

for (var i = 0; i < array.length; i++) {
 var item = array[i];
 if (item.ID == '200') { 
 var index = array.indexOf(item);
 }
}

Answer 11

Here is my take on it, seems like most peoples solutions don't check if the item exists and it removes random values if it does not exist.

First check if the element exists by looking for it's index. If it does exist, remove it by its index using the splice method

elementPosition = array.indexOf(value);
if(elementPosition != -1) {
 array.splice(elementPosition, 1);
}

Answer 12

// Instead Of 
var index = arr.indexOf(200)
// Use 
var index = arr.includes(200);

Please Note: Includes function is a simple instance method on the array and helps to easily find if an item is in the array(including NaN unlike indexOf)

• moto: In addition to this only telling you if it exists, instead of getting the index/item, be cognizant of the compatibility (i.e. no IE): caniuse.com/#search=includes
• Heretic Monkey: includes returns a Boolean indicating if the array contains the value specified.