Download presentation
Presentation is loading. Please wait.
1
JavaScript Functions
2
What is a function? Collection of statements that can be invoked as a unit Because sometimes we want to do more that a single assignment!
3
Output Black Box Inputs
4
Different Types of Functions
Who writes? JavaScript provides Someone else writes & you use You write Frist two today
5
Does function need information?
Alert does…tell it what to write Asking for a random number doesn’t Always need to use () Parameters if data needed () if not
6
Parameters Call a function with a different value every time
MUST give it everything that it expects For alert One parameter, the string to print
7
Return Parameters Function
8
Statement or part of an expression
Alert is a statement; doesn’t give you anything back If you ask for a random number, you expect to get something back
9
Functions as Statements
Performs an action but doesn’t give you anything back Example: alert
10
Alert String to print Function
11
But What if I Want a Value Back?
For calculator: eval(string) Like alert, takes a string as a parameter Does its magic on the string And gives you back a number You can do what you want with the number Put it in an alert Write it out to a form Do more math on it
12
Using eval formname.fieldname.value = eval(‘3+5’); alert(eval(formname.inputfield.value));
13
Format of a Function functionName(parm,parm);
Always needs () even if no parameter functionName();
14
The rules The order of the parameters matter Only a single output
5 - 3 different than 3 -5 Any number of parameters can be defined Fixed for any specific function Only a single output Optional in general But always the same for any specific function More common model
15
JavaScript Functions
16
alert Takes an input value (string) Does not return a value
17
Getting a random number
Math.random() Does not need any inputs Returns a value between 0 and 1
18
Other math functions Take an input value (number)
Math.round(num) Math.floor(num) Math.ceil(num) Take an input value (number) Return a value (number)
19
eval Takes an input value (string) Returns a value (number)
20
Connecting JavaScript to HTML
21
Where Do JavaScript Functions Go?
Like CSS, can be inline or a separate file Like CSS, an external file is considered better practice Like CSS, link to it from the head section
22
A Separate JavaScript File
<script src="myscripts.js"></script> Myscript.js JavaScript option in komodo will work on it next
23
FUNCTION: connecting to HTML
<head> <script src=“function.js”></script> </head> <body> <button type=“button” onclick=“doit();”> </body> HTML file name function name function doit () { alert(“Hi!”); } JAVASCRIPT (function.js)
Similar presentations
