JavaScript

Operators

Arithmetic operators (+ - * / %) do math. Comparison operators (=== !== > <) compare two values and produce a boolean.

Example: why === and not ==

console_check_1 = (0 == "");    // true, surprising!
console_check_2 = (0 === "");   // false, no automatic conversion

const score = 85;
const passed = score >= 50 && score <= 100;
document.getElementById("output").textContent = "Passed: " + passed;

== ("loose equality") silently converts values to a matching type before comparing them, which produces surprising results like the first line above. === ("strict equality") skips that conversion entirely, it compares both value and type, which is almost always what you actually mean. Use === and !== by default; reach for == only if you can explain exactly why you need the automatic conversion.

Combining conditions with logical operators

&& ("and") requires both sides to be true; || ("or") requires at least one; ! negates a single value. The example above uses && to check that a score is both at least 50 and at most 100.

<!DOCTYPE html>
<html>
<body>

  <p id="output"></p>

  <script>
    const score = 85;
    const passed = score >= 50 && score <= 100;

    document.getElementById("output").textContent = "Passed: " + passed;
  </script>

</body>
</html>

← Data Types Conditionals (if / else) →