我们在做web的时候都会用到很多jQuery插件，这些插件可以很方便的使用。但对于初学者来说想要修改插件中的一些功能，或者想要自定义插件却不是容易的事情。自己也刚好在学习这部分的知识，这里用一个案例来介绍jQuery插件的使用和写法。
就拿单页导航这个插件来举例吧，one-page-nav写的比较规范代码也比较短。其他jQuery插件大同小异，学会结构和规范之后自己也可以自定义插件，后面也会讲解对该插件功能的改写，从 会使用-》看懂-》改写-》自定义插件有一个循序渐进的过程。
地址：github：https://github.com/davist11/jQuery-One-Page-Nav
原插件内容：
;(function($, window, document, undefined){ // our plugin constructor var OnePageNav = function(elem, options){ this.elem = elem; this.$elem = $(elem); this.options = options; this.metadata = this.$elem.data('plugin-options'); this.$win = $(window); this.sections = {}; this.didScroll = false; this.$doc = $(document); this.docHeight = this.$doc.height(); }; // the plugin prototype OnePageNav.prototype = { defaults: { navItems: 'a', currentClass: 'current', changeHash: false, easing: 'swing', filter: '', scrollSpeed: 750, scrollThreshold: 0.5, begin: false, end: false, scrollChange: false }, init: function() { // Introduce defaults that can be extended either // globally or using an object literal. this.config = $.extend({}, this.defaults, this.options, this.metadata); this.$nav = this.$elem.find(this.config.navItems); //Filter any links out of the nav if(this.config.filter !== '') { this.$nav = this.$nav.filter(this.config.filter); } //Handle clicks on the nav this.$nav.on('click.onePageNav', $.proxy(this.handleClick, this)); //Get the section positions this.getPositions(); //Handle scroll changes this.bindInterval(); //Update the positions on resize too this.$win.on('resize.onePageNav', $.proxy(this.getPositions, this)); return this; }, adjustNav: function(self, $parent) { self.$elem.find('.' + self.config.currentClass).removeClass(self.config.currentClass); $parent.addClass(self.config.currentClass); }, bindInterval: function() { var self = this; var docHeight; self.$win.on('scroll.onePageNav', function() { self.didScroll = true; }); self.t = setInterval(function() { docHeight = self.$doc.height(); //If it was scrolled if(self.didScroll) { self.didScroll = false; self.scrollChange(); } //If the document height changes if(docHeight !== self.docHeight) { self.docHeight = docHeight; self.getPositions(); } }, 250); }, getHash: function($link) { return $link.attr('href').split('#')[1]; }, getPositions: function() { var self = this; var linkHref; var topPos; var $target; self.$nav.each(function() { linkHref = self.getHash($(this)); $target = $('#' + linkHref); if($target.length) { topPos = $target.offset().top; self.sections[linkHref] = Math.round(topPos); } }); }, getSection: function(windowPos) { var returnValue = null; var windowHeight = Math.round(this.$win.height() * this.config.scrollThreshold); for(var section in this.sections) { if((this.sections[section] - windowHeight) < windowPos) { returnValue = section; } } return returnValue; }, handleClick: function(e) { var self = this; var $link = $(e.currentTarget); var $parent = $link.parent(); var newLoc = '#' + self.getHash($link); if(!$parent.hasClass(self.config.currentClass)) { //Start callback if(self.config.begin) { self.config.begin(); } //Change the highlighted nav item self.adjustNav(self, $parent); //Removing the auto-adjust on scroll self.unbindInterval(); //Scroll to the correct position self.scrollTo(newLoc, function() { //Do we need to change the hash? if(self.config.changeHash) { window.location.hash = newLoc; } //Add the auto-adjust on scroll back in self.bindInterval(); //End callback if(self.config.end) { self.config.end(); } }); } e.preventDefault(); }, scrollChange: function() { var windowTop = this.$win.scrollTop(); var position = this.getSection(windowTop); var $parent; //If the position is set if(position !== null) { $parent = this.$elem.find('a[href$="#' + position + '"]').parent(); //If it's not already the current section if(!$parent.hasClass(this.config.currentClass)) { //Change the highlighted nav item this.adjustNav(this, $parent); //If there is a scrollChange callback if(this.config.scrollChange) { this.config.scrollChange($parent); } } } }, scrollTo: function(target, callback) { var offset = $(target).offset().top; $('html, body').animate({ scrollTop: offset }, this.config.scrollSpeed, this.config.easing, callback); }, unbindInterval: function() { clearInterval(this.t); this.$win.unbind('scroll.onePageNav'); } }; OnePageNav.defaults = OnePageNav.prototype.defaults; $.fn.onePageNav = function(options) { return this.each(function() { new OnePageNav(this, options).init(); }); }; })( jQuery, window , document );
先来看该插件实现的功能有，接下来再讲它是如何实现的。
1：点击导航栏的某一项，内容导航到相应项。当前项的<li>中增加class="current"。
2：鼠标滚动到相应内容时，导航栏中class="current"会切换。
3：其他功能比如说滚动速度和回调函数等。
