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Javascript: variables and parameters
20 March 2014
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What we want to do
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Form with input, button, output
HTML JavaScript
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Add data HTML JavaScript
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Push button and input data sent to javascript
HTML JavaScript
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Javascript uses the data to create a new result
HTML JavaScript
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And moves it to the output location
HTML JavaScript
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How do we do it?
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variables A place to hold a value
Mailbox: know where to pick up my mail; don’t know what’s in it How to define? var name; var name = initial-value;
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Assignment statements
target = new-value; CHANGE the value of the target variable TO the new-value new-value can be a constant, a variable, or an expression x = 3; x = y; x = x+ 5;
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Using values from forms
Value in the form can be treated just like a variable! Giving it a value User input Assign it a value in an onclick Define it in the HTML
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FUNCTION: collection of instructions
HTML JAVASCRIPT (function.js) <head> <script src=“function.js”></script> </head> <body> <button type=“button” onclick=“doit();”> </body> function doit () { alert(“Hi!”); }
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parameters Just a special type of variable
Something that you hand to the function Q: Many users: how do you name? A: Give it its OWN names to use locally Q: How do you match up? A: By POSITION
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FUNCTION with parameters
HTML JAVASCRIPT (function.js) <head> <script src=“function.js”></script> </head> <body> <button type=“button” onclick=“doit(3,5);”> </body> function doit (a,b) { var c = a*b); alert(“product is ”+c); }
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Return value return (value); Want to get information BACK to HTML
With a return, the function has a VALUE Can be used anywhere you can use a constant or variable Alert Assignment statement
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FUNCTION with return HTML JAVASCRIPT (function.js)
<head> <script src=“function.js”></script> </head> <body> <button type=“button” onclick=“alert(doit(3,5));”> </body> function doit (a,b) { var c = a*b); return(c); }
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