function when(conditionFunc, execFunc, interval){
if (conditionFunc()){
execFunc();
}else{
setTimeout(function(){ when(conditionFunc, execFunc, interval);}, interval);
}
}
You have some code which should only execute when a condition is
true. E.g. You have code which relies on a javascript library but can't
be sure the library has loaded yet and don't want the code to execute
until it has. This is common if you have a bookmarklet which injects
more than one <script> tag or you have code which should only execute when an image or other asynchronously loaded element is present. The when
construct lets you sleep periodicially until the condition is true,
then execute the code. I needed this construct a couple of years ago
when I was working on SnapScribe - an online photo book. When I was
working on the Markdown pull-quote bookmarklet I found that sometimes
the bookmarklet wouldn't work because the javascript library it uses
hadn't yet loaded. I knew I'd written something to solve that exact
problem and some digging around the Pixenate codebase later, I found it.
You might find it useful too. This is similar to the following
construct in Java but Javascript doesn't have a Thread.sleep() method...
while (!condition){
Thread.sleep(interval);
}
execFunc()
Use when like this...
function libIsReady(){ return typeof(LIBRARY_NAME) != "undefined" ;};
function useLib(){ // code which uses LIBRARY_NAME methods };
// checks if library has been loaded and if so calls function which uses the library
when (libIsReady, useLib, 2);
... One thing to be careful of; the conditionFunc parameter should be a function not a conditional expression. when
will accept both but if conditionFunc is an expression it will only be
evaluated once so put your conditional expression inside a function and
pass that instead.
