Understanding PHP in_array() Pitfalls and Proper Usage

The in_array() function in PHP checks whether a value exists in an array, but if the third parameter (strict comparison) is omitted the function may produce unintuitive results because it performs loose comparison.

Consider the following PHP code:

<?php
$arr = [true, false];
$f = in_array('Hello', $arr);
if ($f) {
    echo 'in array';
} else {
    echo 'not found';
}
// Output: in array

Even though the string 'Hello' is not present in $arr, the function returns true because the string is loosely compared to true. Adding the strict flag resolves the problem: in_array('Hello', $arr, true) In JavaScript the same issue does not occur; developers typically use indexOf() for array searches, which performs a strict comparison by default.

For a visual illustration of the JavaScript approach, see the accompanying image in the original article.