JavaScript

Data Types

JavaScript's core types: string (text, in quotes), number (JavaScript uses one type for both whole numbers and decimals, no separate "integer" type), boolean (true or false), array (an ordered list), and object (key/value pairs).

Example: checking a value's type

const text = "hello";
const count = 42;
const isReady = true;

document.getElementById("output").textContent =
  typeof text + ", " + typeof count + ", " + typeof isReady;

typeof tells you a value's type at runtime, genuinely useful when a value's type isn't obvious just from reading the code, like data that just arrived from an API response. Try changing count to a string like "42" in the editor and notice how typeof now reports "string", a subtle but real difference that trips up a lot of beginners comparing "42" to 42 later on.

<!DOCTYPE html>
<html>
<body>

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

  <script>
    const text = "hello";
    const count = 42;
    const isReady = true;

    document.getElementById("output").textContent =
      typeof text + ", " + typeof count + ", " + typeof isReady;
  </script>

</body>
</html>

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