How to check if an array index exists or not in javascript?

Question

I am working with Titanium, my code looks like this:

var currentData = new Array();
if(currentData[index]!==""||currentData[index]!==null||currentData[index]!=='null')
{
    Ti.API.info("is exists  " + currentData[index]);
    return true;
}
else
{   
    return false;
}

I am passing an index to the currentData array. I still can't detect a non-existing index using the above code.

Answer 1

Use typeof arrayName[index] === 'undefined'

i.e.

if(typeof arrayName[index] === 'undefined') {
    // does not exist
}
else {
    // does exist
}

Answer 2

var myArray = ["Banana", "Orange", "Apple", "Mango"];

if (myArray.indexOf(searchTerm) === -1) {
  console.log("element doesn't exist");
}
else {
  console.log("element found");
}

Answer 3

These days I would take advantage of ecmascript and use it like that

return myArr?.[index]

Answer 4

This is exactly what the in operator is for. Use it like this:

if (index in currentData) 
{ 
    Ti.API.info(index + " exists: " + currentData[index]);
}

The accepted answer is wrong, it will give a false negative if the value at index is undefined:

const currentData = ['a', undefined], index = 1;

if (index in currentData) {
  console.info('exists');
}
// ...vs...
if (typeof currentData[index] !== 'undefined') {
  console.info('exists');
} else {
  console.info('does not exist'); // incorrect!
}

Answer 5

Someone please correct me if i'm wrong, but AFAIK the following is true:

1. Arrays are really just Objects under the hood of JS
2. Thus, they have the prototype method hasOwnProperty "inherited" from Object
3. in my testing, hasOwnProperty can check if anything exists at an array index.

So, as long as the above is true, you can simply:

const arrayHasIndex = (array, index) => Array.isArray(array) && array.hasOwnProperty(index);

usage:

arrayHasIndex([1,2,3,4],4); outputs: false

arrayHasIndex([1,2,3,4],2); outputs: true

Answer 6

This also works fine, testing by type using === against undefined.

if (array[index] === undefined){ return } // True

Test:

const fruits = ["Banana", "Orange", "Apple", "Mango"];

if (fruits["Cherry"] === undefined){
  console.log("There isn't any cherry in the fruits basket :(")
}

Or similarly:

const fruits = ["Banana", "Orange", "Apple", "Mango"];

if (!fruits["Cherry"]){
  console.log("There isn't any cherry in the fruits basket :(")
}

// No errors: 
if (fruits["Cherry"]){
  console.log("There is some cherry in there!")
}

Answer 7

I had to wrap techfoobar's answer in a try..catch block, like so:

try {
  if(typeof arrayName[index] == 'undefined') {
    // does not exist
  }
  else {
  // does exist
  }
} 
catch (error){ /* ignore */ }

...that's how it worked in chrome, anyway (otherwise, the code stopped with an error).

Answer 8

If elements of array are also simple objects or arrays, you can use some function:

// search object
var element = { item:'book', title:'javasrcipt'};

[{ item:'handbook', title:'c++'}, { item:'book', title:'javasrcipt'}].some(function(el){
    if( el.item === element.item && el.title === element.title ){
        return true; 
     } 
});

[['handbook', 'c++'], ['book', 'javasrcipt']].some(function(el){
    if(el[0] == element.item && el[1] == element.title){
        return true;
    }
});

Answer 9

Consider the array a:

var a ={'name1':1, 'name2':2}

If you want to check if 'name1' exists in a, simply test it with in:

if('name1' in a){
console.log('name1 exists in a')
}else
console.log('name1 is not in a')

Answer 10

var demoArray = ['A','B','C','D'];
var ArrayIndexValue = 2;
if(ArrayIndexValue in demoArray){
   //Array index exists
}else{
   //Array Index does not Exists
}

Answer 11

If you are looking for some thing like this.

Here is the following snippetr

var demoArray = ['A','B','C','D'];
var ArrayIndexValue = 2;
if(demoArray.includes(ArrayIndexValue)){
alert("value exists");
   //Array index exists
}else{
alert("does not exist");
   //Array Index does not Exists
}

Answer 12

If you use underscore.js then these type of null and undefined check are hidden by the library.

So your code will look like this -

var currentData = new Array();

if (_.isEmpty(currentData)) return false;

Ti.API.info("is exists  " + currentData[index]);

return true;

It looks much more readable now.

Answer 13

This way is easiest one in my opinion.

var nameList = new Array('item1','item2','item3','item4');

// Using for loop to loop through each item to check if item exist.

for (var i = 0; i < nameList.length; i++) {
if (nameList[i] === 'item1') 
{   
   alert('Value exist');
}else{
   alert('Value doesn\'t exist');
}

And Maybe Another way to do it is.

nameList.forEach(function(ItemList)
 {
   if(ItemList.name == 'item1')
        {
          alert('Item Exist');
        }
 }

Answer 14

Simple way to check item exist or not

Array.prototype.contains = function(obj) {
    var i = this.length;
    while (i--)
       if (this[i] == obj)
       return true;
    return false;
}

var myArray= ["Banana", "Orange", "Apple", "Mango"];

myArray.contains("Apple")

Answer 15

var fruits = ["Banana", "Orange", "Apple", "Mango"];
if(fruits.indexOf("Banana") == -1){
    console.log('item not exist')
} else {
 console.log('item exist')
}

Answer 16

One line validation. The simplest way.

return !!currentData[index];

Outputs

var testArray = ["a","b","c"]

testArray[5]; //output => undefined
testArray[1]; //output => "b"

!!testArray[5]; //output => false
!!testArray[1]; //output => true

Answer 17

you can simply use this:

var tmp = ['a', 'b'];
index = 3 ;
if( tmp[index]){
    console.log(tmp[index] + '\n');
}else{
    console.log(' does not exist');
}

Answer 18

(typeof files[1] === undefined)?
            this.props.upload({file: files}):
            this.props.postMultipleUpload({file: files widgetIndex: 0, id})

Check if the second item in the array is undefined using the typeof and checking for undefined

Answer 19

if(typeof arrayName[index] == undefined) {
    console.log("Doesn't exist")
}
else {
console.log("does exist")
}

Answer 20

When trying to find out if an array index exists in JS, the easiest and shortest way to do it is through double negation.

let a = [];
a[1] = 'foo';
console.log(!!a[0])   // false
console.log(!!a[1])   // true