Optional Parameters and Default Arguments [StartupCTO]

Last Updated: 17 Nov 2023

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Author: 114.119.133.245

This shows you the differences between two versions of the page.

--- front-end-tech:javascript:optional-parameters-default-arguments [May 23, 2008 11:54 PM]
dordal
+++ front-end-tech:javascript:optional-parameters-default-arguments [Nov 13, 2023 04:07 PM]
111.225.149.10 removed
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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.