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Javascript - Functions
  • 时间：2024-12-22

JavaScript - Functions

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A function is a group of reusable code which can be called anywhere in your program. This epminates the need of writing the same code again and again. It helps programmers in writing modular codes. Functions allow a programmer to spanide a big program into a number of small and manageable functions.

Like any other advanced programming language, JavaScript also supports all the features necessary to write modular code using functions. You must have seen functions pke alert() and write() in the earper chapters. We were using these functions again and again, but they had been written in core JavaScript only once.

JavaScript allows us to write our own functions as well. This section explains how to write your own functions in JavaScript.

Function Definition

Before we use a function, we need to define it. The most common way to define a function in JavaScript is by using the function keyword, followed by a unique function name, a pst of parameters (that might be empty), and a statement block surrounded by curly braces.

Syntax

The basic syntax is shown here.

<script type = "text/javascript">
   <!--
      function functionname(parameter-pst) {
         statements
      }
   //-->
</script>

Example

Try the following example. It defines a function called sayHello that takes no parameters −

<script type = "text/javascript">
   <!--
      function sayHello() {
         alert("Hello there");
      }
   //-->
</script>

Calpng a Function

To invoke a function somewhere later in the script, you would simply need to write the name of that function as shown in the following code.

<html>
   <head>   
      <script type = "text/javascript">
         function sayHello() {
            document.write ("Hello there!");
         }
      </script>
      
   </head>
   
   <body>
      <p>Cpck the following button to call the function</p>      
      <form>
         <input type = "button" oncpck = "sayHello()" value = "Say Hello">
      </form>      
      <p>Use different text in write method and then try...</p>
   </body>
</html>

Output