Javascript Functions

Functions are blocks of code that are separated from the normal flow of your program. You can make "calls" to these blocks of code at anytime. After the execution of the statements in the function is complete, program flow continues at the point where the original call was made.

defining a function

There are four parts needed to define a function: the keyword function, the name, the arguments, and the statements of the function. Below is the format of a function.

function function_name(argument1, argument2,...) { statements; }

The function name should be descriptive and define what the function does. Arguments are incoming values, which the function needs to perform its statements. Some of your functions may not require incoming values, so the argument list is optional. If you omit the arguments, the first line of the function will have format:
function function_name().

calling a function

To call a function, you need to specify the function name followed by a list of the actual values you are sending to the function, if there are any. You may make a call to the function from within the JavaScript section of your code or from within the HTML body. The following examples demonstrate various ways of using functions.

Below is an example of a function whose purpose is to simply print a line. No arguments are needed. The function call is made within the <script> section of the code.

<script language="JavaScript"> <!-- Hide JavaScript code from old browsers function print_line() { document.writeln("I'm printing a line."); } print_line(); // end hiding code --> </script>

Below is a function call from the body of the HTML. Because print_line is a JavaScript component, the function call needs to be nested inside another set of <script> tags. Without it, the browser would simply print print_line("I'm printing another line."); onto the screen. This example also shows how to use an argument in the function. In the function call, I am sending the string "I'm printing another line." to the function. The function calls this string "message." It then prints message.

<script language="JavaScript"> <!-- Hide JS code from old browsers function print_line(message) { document.writeln(message); } // end hiding code --> </script> <body> <script> print_line("I'm printing another line."); </script> </body>

Not only can a function accept incoming values, but it can also return a value back to the function call. In the example below, the function call is the right side of an assignment statement. The variable total gets the value that is returned from the function calc_total. The function call sends three values to the calc_total; 1, 2, and 3. The function renames these values number1, number2, and number3. The variable, answer, gets the sum of the three numbers. The function then returns the value of the variable answer.

<script language="JavaScript"> <!-- Hide JS code from old browsers function calc_total(number1, number2, number3) { var answer; answer = number1 + number2 + number3; return answer; } var total; total = calc_total(1, 2, 3); document.writeln(total); // end hiding code --> </script>

Intro         Variables         Statements         If then else

Loops         Objects         Functions

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