What is the difference between `==` and `===`?

=== compares value and type without converting anything (strict equality). == converts the types before comparing (loose equality with coercion). The recommendation is to always use ===.

• === (strict equality): it only returns true if both values are of the same type and have the same value. It does no conversion.
• == (loose equality): if the types differ, JavaScript tries to convert them to a common type before comparing. This produces surprising results.

That's why the general recommendation is to use ===: it's predictable and avoids errors.

// === compares value and type
console.log(5 === 5);       // true
console.log(5 === "5");     // false (number vs string)

// == converts the types before comparing
console.log(5 == "5");      // true  ("5" is converted to 5)
console.log(0 == false);    // true  (false is converted to 0)
console.log("" == false);   // true  (both are converted to 0)
console.log(null == undefined); // true (special case)

// Cases that are confusing with ==
console.log([] == false);   // true
console.log(" " == 0);      // true (the space is converted to 0)

// With === everything is more predictable
console.log(0 === false);   // false
console.log(null === undefined); // false

Using == "because it works" in simple cases and then running into weird bugs like [] == false being true. The coercion rules of == are hard to remember and lead to subtle errors.

"=== is strict equality: it compares value and type without converting. == is loose equality: if the types don't match, JavaScript converts one of them before comparing, which produces unexpected results like 0 == false being true. I always use === because it's predictable; I would only use == on purpose for a specific case, like valor == null to check for null and undefined at the same time."