JavaScript · Language basics

var

Function-scoped and hoisted. Kept for legacy code; use let or const instead.

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Syntax

var x = 1;

Example

Try it

function demo() {
  if (true) { var x = 1; }
  console.log(x);
}
demo();

var leaks out of blocks and initialises as undefined before its declaration.

Reference pages are the quick answer. The course explains the why, shows the full example and ends with a challenge.