Plugins extend jQuery.fn so $('#list').myPlugin(options) works everywhere. Legacy sites bundle dozens—date pickers, modals, tables—sharing the same pattern.
Minimal plugin shape
$.fn.highlight = function () {
return this.each(function () { $(this).css('background', '#fef3c7'); });
};Namespacing events
Bind .on('click.myplugin') and tear down with .off('.myplugin') on destroy—prevents duplicate handlers when Ajax re-renders partials.
Maintenance
Before upgrading jQuery major versions, check plugin compatibility matrices—unmaintained plugins are a common blocker.
Self-check
- What should a plugin return for chaining?
- How remove all plugin listeners?
Challenge
Mini plugin
- Run code and click the button.
- Plugin method changes card style.
Done when: highlight plugin runs without errors.
Pitfall: Plugins that store state on elements without namespacing events leak memory on SPAs—namespace with .on("click.myplugin").
Interview prep
- How do jQuery plugins extend fn?
$.fn.myPlugin = function() { return this.each(...) }—returnthisfor chainability and namespace events.