Hoisting¶

Hoisting consists in bringing up [scope] (scope_zakres_variety.md) declaration [variables] (variables.md). This mechanism is only for variables declared with the var keyword and function declaration. This means that we can call a function or use such a variable before its declaration.

The following examples show this mechanism:

console.log(foo);
var foo = "Lorem ipsum";

In the example above, the console will display undefined.

In turn, in the next example:

foo = 'hello'
console.log(foo);
var foo = 'Lorem ipsum';
console.log(foo)

add = function(a, b) {
  return a + b;
}
console.log(add(2, 3)); // on the console screen we will see 5, even though we declare the add variable in the next line of code
var add;

In turn trying to hoisting with a variable declared with let:

console.log(foo);
let foo = "Lorem ipsum";

we will get the error: Uncaught ReferenceError: Cannot access 'foo' before initialization.