JavaScript Type Coercion

Written by Swapnil RajaPublished 24 Aug 2026

Type coercion is JavaScript converting types automatically, whether you wanted it or not.

It is the reason "5" + 3 and "5" - 3 give completely different answers.

Understanding it removes most of JavaScript's reputation for strangeness.

Example

javascript

console.log("5" + 3);
console.log("5" - 3);

The output is 53 then 2.

Plus joined them; minus converted them.

Why It Happens

Most operators expect numbers, so they convert what they are given.

+ is the exception: if either side is a string, it joins instead.

PreviousJavaScript Type Conversion NextJavaScript == vs ===

Complete Example

html

<!DOCTYPE html>
<html>
<head>
  <title>JavaScript Type Coercion</title>
</head>
<body>

  <h1>Type Coercion</h1>

  <p id="out"></p>

  <script>
    const lines = [
      '"5" + 3 = ' + ("5" + 3),
      '"5" - 3 = ' + ("5" - 3),
      'true + 1 = ' + (true + 1),
      '1 + "2" = ' + (1 + "2"),
      'Number("5") + 3 = ' + (Number("5") + 3)
    ];

    document.getElementById("out").innerHTML = lines.join("<br>");
  </script>

</body>
</html>

JavaScript Type Coercion

Example

Why It Happens

Syntax

The Plus Operator

Example

Every Other Operator Converts

Example

Booleans Become Numbers

Example

The Famous Oddities

Example

How to Avoid Surprises

Example

Complete Example

Try It Yourself

Important Points

Conclusion