What is the difference between == and === in JavaScript?

== vs ===

Both == and === check the types of their operands. The difference is in how they respond if the types don't match. The == allows coercion when types don't match and === disallows coercion.

// == Examples (loose equality)
5 == "5"    // true (string "5" is converted to number 5)
0 == false  // true (false is converted to number 0)
null == undefined  // true
[] == false // true (both are converted to 0)

// === Examples (strict equality)
5 === "5"    // false (different types)
0 === false  // false (different types)
null === undefined  // false
[] === false // false

As a best practice, it's generally recommended to use === because:

• It's more predictable since no type conversion occurs
• It helps prevent subtle bugs caused by unexpected type coercion
• It makes your code's intentions clearer

Always use triple equals, ===, unless you have a specific reason to use ==. The only time you might want to use == is when you specifically want type coercion, but those cases are rare and should be clearly documented.