Calling Your Own Functions

JavaScript Tutorials - Herong's Tutorial Examples

∟Calling Your Own Functions - Example

This section provides a quick description of how to call your own JavaScript functions and a tutorial example of calling temperature conversion function.

Once a function is defined, you can call it as part of an expression as shown in this syntax format:

   ... function_name(exp1, exp2, ...) ...;
}

When the above expression is evaluated, the following steps will be followed:

Step 1. The specified parameter expressions will be evaluated into primitive values or object references before passing them into the function body.
Step 2. The body of the specified function will be executed.
Step 3. The return value is collected and it will be used to evaluate the rest of the calling expression.

Here is a tutorial example that defines a simple function to convert a temperature value in Fahrenheit to Celsius:

<html>
<!-- Define_Call_Functions.html
   Copyright (c) 2008 HerongYang.com. All Rights Reserved.
-->
<head><title>Define and Call Functions</title></head>
<body>
<pre>
<script type="text/javascript">
// Defining a new function
function f2c(fahrenheit) {
   document.write("Converting Fahrenheit = "+fahrenheit+"\n");
   var celsius = (fahrenheit - 32.0 ) / 1.8;
   document.write("Returning Celsius = "+celsius+"\n");
   return celsius;
}

// Calling the new function
   var received;
   
   document.write("\nTest 1:\n");
   received = f2c(70.0)
   document.write("Received Celsius = "+received+"\n");
   
   document.write("\nTest 2:\n");
   received = f2c(212.0)
   document.write("Received Celsius = "+received+"\n");
   
   document.write("\nTest 3:\n");
   received = f2c(0.0)
   document.write("Received Celsius = "+received+"\n");
</script>
</pre>
</body>
</html>

The output of this tutorial example shows no surprises:

Test 1:
Converting Fahrenheit = 70
Returning Celsius = 21.11111111111111
Received Celsius = 21.11111111111111

Test 2:
Converting Fahrenheit = 212
Returning Celsius = 100
Received Celsius = 100

Test 3:
Converting Fahrenheit = 0
Returning Celsius = -17.77777777777778
Received Celsius = -17.77777777777778