Front-End Web Development: The Big Nerd Ranch Guide (opal opal parris' Library) by Chris Aquino & Todd Gandee

Author:Chris Aquino & Todd Gandee [Aquino, Chris]
Language: eng
Format: epub
Tags: Big Nerd Ranch Guides, COM060160, Front-End Web Programming
ISBN: 9780134432533
Publisher: Big Nerd Ranch Guides
Published: 2016-07-29T04:00:00+00:00

When you registered the event handler callback with this.$element.on, you specified click as the event name. But you also passed in a filtering selector as the second argument. The filtering selector tells the event handler to run the callback function only if the event was triggered by an <input> element.

This is a pattern called event delegation. It works because some events, like clicks and keypresses, propagate through the DOM, meaning each ancestor element is informed about the event.

Any time you need to listen for an event on elements that are dynamically created and removed, such as the checklist items, you should use event delegation. It is easier and more performant to add a single listener to the dynamic elements’ container and then run the handler function based on what element triggered the event.

Notice that you do not call event.preventDefault inside the event handler. Why not? If you called event.preventDefault, the checkbox would not actually change its visual state to show a checkmark in the box.

Also, notice that you bind the event handler callback to this, which refers to the instance of CheckList.

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