<!DOCTYPE HTML>
<html>
<body>
<p>Before the script...</p>
<script>
alert([[25,4]].includes([25,4]));
</script>
<p>...After the script.</p>
</body>
</html>
When I run the above code, it outputs "false", which isn't correct. If I change [[25,4]].includes([25,4]) to ['a'].includes('a'), it outputs the correct answer "true". Why does it do that?
That's because [25,4] !== [25,4] as the two operands refer to 2 different array objects. JavaScript do no consider 2 different objects equal. ['a'].includes('a') returns true as 'a' is a string (primitive value.) If you convert the 'a' into a String object the .includes method should return false. (Check What is the difference between JavaScript object and primitive types?)
'a' === 'a' // true
new String('a') === new String('a') // false
[new String('a')].includes(new String('a')) // false
The .includes method should return true if you change your code into:
const item = [25,4];
const array = [item];
console.log(array.includes(item)); // true
String object say a:string with value abc contains a?
includestests for strict equality meaning the two arrays would need to be the same array not two arrays that happen to hold the same values. It doesn't work for the same reason[[25,5]] === [[25,5]]is false.var tuple = [25, 24]; alert([tuple].includes(tuple))there you go