Referring to custom objects in functions driven by setTimeout

[philcha]

I've had lots of fun(!!??) with setTimeout, especially in conjunction with objects.<br><br>setTimeout has 2 arguments:<br>*&nbsp;&nbsp;a string which is interpreted (effectively by an eval function) on expiry of the timeout.<br>*&nbsp;&nbsp;the timeout interval.<br><br>Because the first argument is treated as a string, it's very difficult to see what's being evaluated.&nbsp;&nbsp;Generally when I use setTimeout I:<br>*&nbsp;&nbsp;build the string in a variable so if I have problems I can use an alert to display it and check it.<br>*&nbsp;&nbsp;use the string as the 1st agrumentof setTimeout, e.g. setTimeout(myString, interval);<br><br>Also because the first argument is treated as a string, on expiry of the timeout the browser does not remember any object references (&quot;this&quot; or &quot;myObj&quot which were valid at the time of the setTimeout call.<br><br>So in the simplest case you have to hardcode the actual name of the variable which contains the object reference in the function driven by the setTimeout call, e.g.<br>var myObj = new myObjType;&nbsp;&nbsp;// object constructor<br>setTimeout (myFunc, interval);<br>function myFunc(){<br>&nbsp;&nbsp;&nbsp;myObj.width = x;<br>}<br><br>If you want to use myFunc on a range of objects or to make the entire sequence of code which calls myFunc re-usable, things get trickier and you have to:<br>// Make the OBJECT on which myFunc operates a custom <br>// PROPERTY of a standard JS object, e.g.<br>var myObj = new myObjType;<br>document.ObjId = myObj;<br>// Create a function to call myFunc.&nbsp;&nbsp;All application code <br>// calls callMyFunc, never myFunc<br>function callMyFunc(newWidth, interval){&nbsp;&nbsp;<br>&nbsp;&nbsp;&nbsp;var myString = &quot;myFunc(&quot; + newWidth + &quot;, &quot; + interval + <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&quot&quot;;<br>&nbsp;&nbsp;&nbsp;// This where it's handy to be able to display myString <br>&nbsp;&nbsp;&nbsp;// if you're finding it difficult to get the punctuation <br>&nbsp;&nbsp;&nbsp;// right&nbsp;&nbsp;-&nbsp;&nbsp;especially if there are several arguments <br>&nbsp;&nbsp;&nbsp;// and&nbsp;&nbsp;/ or some of the arguments are string values and <br>&nbsp;&nbsp;&nbsp;// have to be in single quotes.<br>&nbsp;&nbsp;&nbsp;&nbsp;setTimeout (myString, interval);<br>}<br>// Refer to the target object via the custom property of <br>// the standard object, e.g.<br>function myFunc(newWidth, interval){<br>&nbsp;&nbsp;&nbsp;// Here you have to use ObjId to find the required object<br>&nbsp;&nbsp;&nbsp;// see notes below.<br>&nbsp;&nbsp;&nbsp;document.ObjId.width = newWidth;<br>}<br>