JavaScript Function

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A JavaScript Function is a block of code designed to perform a particular task.

The main advantages of using JavaScript Function :

• Code reuse: Define the code once, and use it many times.
• Use the same code many times with different arguments, to produce different results.

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JavaScript Function Example

Let’s see the simple example of function in Java Script that does not has arguments.

<script>

function msg(){

alert("hello! this is message");

}

</script>

<input type="button" onclick="msg()" value="call function"/>

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Function Parameter

Functions can take parameters. Function parameters are the names listed in the function’s definition.

 function sayHello(name) {

   alert("Hi, " + name);

}



sayHello("David");

//Alerts "Hi, David"

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Multiple Parameter

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

When calling the function, provide the arguments in the same order in which you defined them.

 function sayHello(name, age) {

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

}



sayHello("John", 20)

//Outputs "John is 20 years old."

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Return Function

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

This statement is useful when making calculations that require a result.

  function addNumbers(a, b) {

   var c = a+b;

   return c;

}

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

//Outputs 42