[ES2016] Check if an array contains an item using Array.prototype.includes

We often want to check if an array includes a specific item. It's been common to do this with the Array.prototype.indexOf method, but now we have a simpler way: We can use the Array.prototype.includes method, which is available starting with ES2016.

 

Normal case:

var a = [1, 2, 3];
a.includes(2); // true 
a.includes(4); // false

 

Search from index:

[1, 2, 3].includes(3, 3);  // false
[1, 2, 3].includes(3, -1); // true

 

NaN problem:

[1, 2, NaN].includes(NaN); // true
[1, 2, NaN].indexOf(NaN); // -1