Do JavaScript arrays have an equivalent of Python’s “if a in list”?

Question

If I have a list in Python, I can check whether a given value is in it using the in operator:

>>> my_list = ['a', 'b', 'c']

>>> 'a' in my_list
True

>>> 'd' in my_list
False

If I have an array in JavaScript, e.g.

var my_array = ['a', 'b', 'c'];

Can I check whether a value is in it in a similar way to Python’s in operator, or do I need to loop through the array?

In other words, I’m asking [this question](http://stackoverflow.com/questions/1529986/ruby-methods-equivalent-of-if-a-in-list-in-python), but for JavaScript instead of Ruby. — Paul D. Waite, Sep 16 '11 at 09:45
possible duplicate: http://stackoverflow.com/questions/237104/array-containsobj-in-javascript — mouad, Sep 16 '11 at 09:48
@6502: ah, that’s the stuff. Write that up into an answer and the points are yours. — Paul D. Waite, Sep 16 '11 at 09:48
Check [this](http://stackoverflow.com/questions/237104/array-containsobj-in-javascript) qeustion. — denolk, Sep 16 '11 at 09:49
@mouad: great spot — I’m actually using underscore.js, which the top answer to that question mentions, so I might use their function for this. — Paul D. Waite, Sep 16 '11 at 09:49

score 31 · Answer 1 · edited Feb 24 '23 at 15:21

31

Since ES7, it is recommended to use includes() instead of the clunky indexOf().

var my_array = ['a', 'b', 'c'];

my_array.includes('a');  // true

my_array.includes('dd'); // false

edited Feb 24 '23 at 15:21

FZs

answered Feb 26 '19 at 19:59

Daniel Kim

score 15 · Accepted Answer · answered Sep 16 '11 at 09:47

15

var my_array = ['a', 'b', 'c'];
alert(my_array.indexOf('b'));
alert(my_array.indexOf('dd'));

if element not found, you will receive -1

answered Sep 16 '11 at 09:47

Peter Porfy

2

In modern browser, yes, but older internet explorers does not support it. Here is a question about it (and the workaround): http://stackoverflow.com/questions/2790001/fixing-javascript-array-functions-in-internet-explorer-indexof-foreach-etc – Peter Porfy Sep 16 '11 at 09:57
what if searched item exists more than one in an array ? – Ciasto piekarz Dec 28 '18 at 17:32
@Ciastopiekarz indexOf returns the first occurrence: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/indexOf – Peter Porfy Dec 28 '18 at 18:05

score 3 · Answer 3 · edited Jun 07 '18 at 23:32

3

var IN = function(ls, val){
    return ls.indexOf(val) != -1;
}

var my_array = ['a', 'b', 'c'];
IN(my_array, 'a');

edited Jun 07 '18 at 23:32

J. Doe

answered Dec 02 '15 at 12:51

score 1 · Answer 4 · edited Feb 24 '23 at 15:20

1

The most current way with ES7 would be the following:

let myArray = ['a', 'b', 'c'];

console.log(myArray.includes('a'))

This will return true or false.

edited Feb 24 '23 at 15:20

FZs

answered Aug 16 '20 at 20:40

Alex Lytle

4 Answers4