Type Coercion & typeof

Understand why JavaScript silently converts types, how to check types with typeof, and how to convert values explicitly.

Step 1 of 5

Why "5" + 3 equals "53"

When you use an operator on two values of different types, JavaScript doesn't just give up — it tries to help by converting one value to match the other. This automatic conversion is called type coercion.

The most infamous example: `"5" + 3` gives you `"53"`, not `8`. Why? The `+` operator works for both addition (numbers) and concatenation (strings). When one side is a string, JavaScript assumes you meant concatenation and converts the number to a string. So `"5" + 3` becomes `"5" + "3"`, which is `"53"`.

But with other operators like `-`, `*`, and `/`, strings get converted to numbers: `"5" - 3` gives `2`, because subtraction only makes sense with numbers. This inconsistency is one of the most common sources of bugs in JavaScript.

Think of it this way: Type coercion is like JavaScript being an overly helpful translator — it guesses what you meant, but sometimes it guesses wrong. Imagine telling a friend '5 plus 3' in a noisy room, and they hear 'five and three' and write '53' on paper. They tried to help, but misunderstood the operation.

Web Standard

Type coercion follows a precise set of rules defined in the ECMAScript specification. The `+` operator checks: if either operand is a string, convert the other to a string and concatenate. For `-`, `*`, `/`, and `%`, both operands are converted to numbers. These rules are consistent, even if the results seem surprising.

Learn more on MDN

Type coercion

JAVASCRIPTREAD ONLY

CONSOLE

Click "Run" to execute your code...