A Meteor.js utility function to easily attach a function to a given template's "rendered" callback but only run it once, on the next render.

renderOnce.js

// Useful for occasions on which you know that an action will result in the re-rendering of a template
// (through invalidation) and you want to execute task(s) once the rendering is complete in response.
// Sometimes, you only need to execute these task(s) in response to that specific action, so it doesn't
// make sense to add the task(s) to the normal "rendered" callback and then test if they need to be executed
// every time the template is rendered.
renderOnce = function(template, oneTimeFunc, afterwards) {
        // template:    either a Meteor Template instance, or the string name of such an instance
        // oneTimeFunc: the function you are attaching to the "rendered" callback to be run only once
        // afterwards:  set to true if you need the oneTimeFunc to be executed after the normal "rendered" callback,
        //              rather than before it
        var oldRender;
	if (typeof template === "string") template = Template[template];
	if (!template) return false;
	oldRender = template.rendered;
	template.rendered = function() {
		if (afterwards) {
			oldRender && oldRender.apply(this, arguments);
			oneTimeFunc.apply(this, arguments);
		}
		else {
			oneTimeFunc.apply(this, arguments);
			oldRender && oldRender.apply(this, arguments);			
		}
		template.rendered = oldRender;
	}
	return true;
};