[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 = [, , ];
a.includes(); // true
a.includes(); // false

Search from index:

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

NaN problem:

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