Function are subprograms which are used to compute a value or perform a task.

Type of Function

– Library or Built-in functions Ex: – valueOf( ) , write( ), alert( ) etc

– User-defined functions

Example

Rules

• Function name only starts with a letter, an underscore ( _ ).
• Function name cannot start with a number.
• Do not use reserved keywords. e.g. else, if etc.
• Function names are case-sensitive in JavaScript.

How Function Call Works

The code inside a function isn‟t executed until that function is called.