Last Updated: 17 Nov 2023

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Author: 114.119.133.245

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front-end-tech:javascript:optional-parameters-default-arguments [May 23, 2008 11:54 PM]
dordal 		front-end-tech:javascript:optional-parameters-default-arguments [Nov 17, 2023 04:00 PM]
114.119.133.245 old revision restored (Oct 7, 2023 07:10 PM)
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 += Optional Parameters and Default Arguments =
  
 +JavaScript supports optional parameters and default arguments to functions, but only supports the latter with a bit of a hack.
 +
 +Optional parameters are easy. Just define a function to and then don't pass all the parameters:
 +<code>
 +function testFunction(a,b,c) {
 +   document.write(a + " ");
 +   document.write(b + " ");
 +   document.write(c + " ");
 +}
 +
 +testFunction('foo','bar');   // will print 'foo bar undefined '
 +</code>
 +
 +Of course, your function must handle those undefined parameters. You might want to set defaults for any parameters that are undefined; to do this, just check if they
 +are undefined:
 +<code javascript>
 +function testFunction(a,b,c) {
 +   // this says 'if the type of a is undefined, set it to '', otherwise set it 
 +   // to a (e.g. itself)'
 +   a = (typeof(a) == undefined) ? '' : a;   
 +   b = (typeof(b) == undefined) ? '' : b;     
 +   c = (typeof(b) == undefined) ? '' : c;
 +}
 +</code>
 +
 +One other thing that you can do is check the length (or values) of the ''arguments'' array. The ''arguments'' array is set inside each function, and contains a list of the arguments passed to the function.