How to find the array index with a value?

How to find the array index with a value?

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.

Solutions/Answers:

Solution 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.

Solution 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

Solution 3:

Use jQuery’s function
jQuery.inArray

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

Solution 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.

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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);

Solution 5:

Use indexOf

imageList.indexOf(200)

Solution 6:

how about indexOf ?

alert(imageList.indexOf(200));