Scope of variable – Javascript

Scope specifies the accessibility of a variable in a program.

Javascript variables have 3 scope

1. Local
2. Global
3. Automatically Global

Local scope

A variable declared inside a function. These variables can be accessed (used) only inside the function where it is declared, not outside of it.

<script>
function demo() {
    // Local variable
    var x = 12; 
}
</script>

Global scope

A variable declared outside of a function. These variables can be accessed anywhere in the script and in webpage.

<script>
// Global Variable
var x  ="Hello";
function demo() {
	alert(x);
}
</script>

All javascript global variables belongs to Window object.

Automatically Global

A variable becomes automatically global, when is assigned a value without being declared.

<script>

function demo() {
    x = 12; 
}
demo();
document.write(x);
</script>

Lifetime of variables – javascript

Lifetime of a variable in javascript depends on the scope of a variable.

1. Local variable lifetime starts inside a function & ends when the function execution is completed.
2. Global variable lifetime ends when the webpage is closed.