Determine whether an array contains a value
Determine whether an array contains a value
Question
I need to determine if a value exists in an array.
I am using the following function:
Array.prototype.contains = function(obj) {
var i = this.length;
while (i--) {
if (this[i] == obj) {
return true;
}
}
return false;
}
The above function always returns false.
The array values and the function call is as below:
arrValues = ["Sam","Great", "Sample", "High"]
alert(arrValues.contains("Sam"));
Accepted Answer
var contains = function(needle) {
// Per spec, the way to identify NaN is that it is not equal to itself
var findNaN = needle !== needle;
var indexOf;
if(!findNaN && typeof Array.prototype.indexOf === 'function') {
indexOf = Array.prototype.indexOf;
} else {
indexOf = function(needle) {
var i = -1, index = -1;
for(i = 0; i < this.length; i++) {
var item = this[i];
if((findNaN && item !== item) || item === needle) {
index = i;
break;
}
}
return index;
};
}
return indexOf.call(this, needle) > -1;
};
You can use it like this:
var myArray = [0,1,2],
needle = 1,
index = contains.call(myArray, needle); // true
Popular Answer
jQuery has a utility function for this:
$.inArray(value, array)
Returns index of value
in array
. Returns -1
if array
does not contain value
.
See also How do I check if an array includes an object in JavaScript?
Read more… Read less…
This is generally what the indexOf() method is for. You would say:
return arrValues.indexOf('Sam') > -1
Array.prototype.includes()
In ES2016, there is Array.prototype.includes()
.
The
includes()
method determines whether an array includes a certain element, returningtrue
orfalse
as appropriate.
Example
["Sam", "Great", "Sample", "High"].includes("Sam"); // true
Support
According to kangax and MDN, the following platforms are supported:
- Chrome 47
- Edge 14
- Firefox 43
- Opera 34
- Safari 9
- Node 6
Support can be expanded using Babel (using babel-polyfill
) or core-js
. MDN also provides a polyfill:
if (![].includes) {
Array.prototype.includes = function(searchElement /*, fromIndex*/ ) {
'use strict';
var O = Object(this);
var len = parseInt(O.length) || 0;
if (len === 0) {
return false;
}
var n = parseInt(arguments[1]) || 0;
var k;
if (n >= 0) {
k = n;
} else {
k = len + n;
if (k < 0) {k = 0;}
}
var currentElement;
while (k < len) {
currentElement = O[k];
if (searchElement === currentElement ||
(searchElement !== searchElement && currentElement !== currentElement)) {
return true;
}
k++;
}
return false;
};
}
It's almost always safer to use a library like lodash simply because of all the issues with cross-browser compatibilities and efficiency.
Efficiency because you can be guaranteed that at any given time, a hugely popular library like underscore will have the most efficient method of accomplishing a utility function like this.
_.includes([1, 2, 3], 3); // returns true
If you're concerned about the bulk that's being added to your application by including the whole library, know that you can include functionality separately:
var includes = require('lodash/collections/includes');
NOTICE: With older versions of lodash, this was _.contains()
rather than _.includes()
.
tl;dr
function includes(k) {
for(var i=0; i < this.length; i++){
if( this[i] === k || ( this[i] !== this[i] && k !== k ) ){
return true;
}
}
return false;
}
Example
function includes(k) {
for(var i=0; i < this.length; i++){
if( this[i] === k || ( this[i] !== this[i] && k !== k ) ){
return true;
}
}
return false;
}
function log(msg){
$('#out').append('<div>' + msg + '</div>');
}
var arr = [1, "2", NaN, true];
arr.includes = includes;
log('var arr = [1, "2", NaN, true];');
log('<br/>');
log('arr.includes(1): ' + arr.includes(1));
log('arr.includes(2): ' + arr.includes(2));
log('arr.includes("2"): ' + arr.includes("2"));
log('arr.includes(NaN): ' + arr.includes(NaN));
log('arr.includes(true): ' + arr.includes(true));
log('arr.includes(false): ' + arr.includes(false));
#out{
font-family:monospace;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id=out></div>
Longer Answer
I know this question isn't really about whether or not to extend built-in objects, but the attempt of the OP and the comments on this answer highlight that debate. My comment from Feb 12, '13 cites an article that outlines this debate really well, however that link broke and I can't edit the original comment because too much time has passed, so I include it here.
If you're looking to extend the built-in Array
object with a contains
method, probably the best and most responsible way to do this would be to use this polyfill from MDN. (See also this section of the MDN article on Prototypical inheritance, which explains that "The only good reason for extending a built-in prototype is to backport the features of newer JavaScript engines; for example Array.forEach, etc.")
if (!Array.prototype.includes) {
Array.prototype.includes = function(searchElement /*, fromIndex*/ ) {
'use strict';
var O = Object(this);
var len = parseInt(O.length) || 0;
if (len === 0) {
return false;
}
var n = parseInt(arguments[1]) || 0;
var k;
if (n >= 0) {
k = n;
} else {
k = len + n;
if (k < 0) {k = 0;}
}
var currentElement;
while (k < len) {
currentElement = O[k];
if (searchElement === currentElement ||
(searchElement !== searchElement && currentElement !== currentElement)) {
return true;
}
k++;
}
return false;
};
}
Don't want strict equality, or want to choose?
function includes(k, strict) {
strict = strict !== false; // default is true
// strict = !!strict; // default is false
for(var i=0; i < this.length; i++){
if( (this[i] === k && strict) ||
(this[i] == k && !strict) ||
(this[i] !== this[i] && k !== k)
) {
return true;
}
}
return false;
}