A JavaScript function is a block of code designed to perform a particular task.
It is executed when something invokes it (calls it)
It is defined with a function key world followed by a name followed by parentheses ()
Function myFunction (s1,s2) {return s1*s2 //the function}
Function names can contain letters , digits , underscore, and dollar signs (same rules as variables)
The parentheses may include parameter names separated by commas so the code to be executed by the function, is placed inside curly brackets : {}
Invoking function
The code inside the function will execute when “something” invokes the function
- When an event occurs exemple , on button click
- When it is called from javascritp code
- Automatically , self invoked
Function Return
When JavaScript reaches a return statement , the function will stop executing.
If the Function was invoked from a statement , JavaScript will “return” to execute the code after the invoking statement .
Functions often compute a return value . The return value is “returned” back to the “caller”
Functions can be used as Variable Values
Function can be used the same way as you use variables , in all types of formulas , assignements and calculations .
Instead of using a variable to store the return of a function :
var x = toCelsius(88);
var text = "the temperature is "+ x + "Celsius";
Or you can use the function directly , as a variable value :
var text = "the temperature is "+ toCelsius(88)+ "Celsius";
Local & Global variables
The scope of a variable is the region of your program in which it is defined
JavaScript Variables have only two scopes : Local Variable or Global Variable
Global variable
Local Variable
That’s all you need to know to get started with JavaScript function !
