JavaScript Functions

Java Script function is a block of code designed to perform a particular task. the main advantage of using functions code reuse define the code once and use it many times.

function name (){

// code to be executed

}

Note: function names can contain letters, digits, underscores, and dollar signs (same rules as variables)

Calling a Function

To execute the function, you need to call it. to call a function, start with the name of the function, then follow it with the arguments in parentheses.

Example:

function myFunction(){

alert(“Calling a function !”)

}

myFunction();

Note: always number the ends of the calling function with; a semicolon.

Function myFunction(){

alert(“Alert box !);

}

myFunction();

// “Alert box !”

// “Some other code”

myFunction();

// “Alert box !”

Note: you can also call a function using this syntax: myFunction.calling the difference is that when calling in this way, you are passing the ‘this ‘ keyword to a function. you will learn about it later

Function Parameters:

A function can take Parameters.

FunctionName(Pr1, Pre2, Pre3){

//code

}

Using Parameters:

function sayHello(name){

ALEART(“Hi,” + name);

}

sayHello(“Billo”)

Output: Hi Billo

Multiple Parameters:

we can define multiple parameters for a function by comma-separating them

function myFunc{

//——-

}

Example:

function test(x,y){

if(x>y){

document.write(x);

}

else{

document.write(y);

}

}

test(5,8);

Output: 8

Example:

function sayHello(name,age){

document.write(name+”is”+age+”years old.”);

}

sayHello(“Billo”35)

Output: Billo is 35 years old.

Function Return:

A function can have an optional return statement. it is used to return a value from the function.

This statement is useful when making evaluations that require a result

Example:

function myFunction(b,g){

return b*g;

}

var x = myfunction(35,30);

//Return value will end up in x

Output: 1050

Example: function addNumber(b,g){

var z = b+g;

return z;

}

document.write(addNumber(40,2));

JavaScript Alert Box:

JavaScript offers three types of popup boxes, the Alert, Prompt, and Confirm boxes.

Alert Example:

alert(“Do you really want to leave this page ?”);

output: Do you really want to leave this page?

Ok

To display line break: alert (“Hello\nHow are you?”);

output: Hello

How are you?

Ok

Prompt Box: Prompt box is often used to have the user input

Example:

var users = prompt(“Please enter your name “);

alert(user);

Confirm Box: A confirm box is after used to have the user verify or accept something.

Example:

var result = confirm (“Do you really want to leave this page? “);

if(result == true){

alert (“Thanks for visiting”);

}

else{

alert(“Thanks for staying with us”);

}