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目录
[1]原理介绍 [2]数字加减 [3]元素尺寸[4]内容滚动
前面的话
当元素内容溢出元素尺寸范围时，会出现滚动条。但由于滚动条在各浏览器下表现不同，兼容性不好。所以，模拟滚动条也是很常见的应用。本文将详细介绍滚动条模拟
原理介绍
滚动条模拟实际上和元素模拟拖拽类似。仅仅通过范围限定，使元素只可以在单一方向上拖拽
<div id="box" style="height: 200px;width: 16px;background-color:#F5F5F5;border-radius:10px;box-shadow:inset 0 0 6px rgba(0,0,0,0.3);position:relative;"> <div id="test" style="height: 60px;width: 16px;background-color:#555;box-shadow:inset 0 0 6px rgba(0,0,0,.3);border-radius:10px;position:absolute;"></div></div><script>test.onmousedown = function(e){ e = e || event; var that = this; var disY = e.clientY - this.offsetTop; document.onmousemove = function(e){ e = e || event; var T = e.clientY - disY; if(T < 0){T = 0;} var TMax = parseInt(box.style.height) - that.offsetHeight; if(T > TMax){T = TMax;} that.style.top = T + 'px'; } document.onmouseup = function(){ document.onmousemove = null; //释放全局捕获 if(test.releaseCapture){test.releaseCapture();} } //IE8-浏览器阻止默认行为 if(test.setCapture){test.setCapture();} //阻止默认行为 return false;}</script> 通过将上面代码封装成函数，可以实现横向和纵向两种滚动条
<div id="box1" style="height: 200px;width: 16px;background-color:#F5F5F5;border-radius:10px;box-shadow:inset 0 0 6px rgba(0,0,0,0.3);position:relative;"> <div id="test1" style="height: 60px;width: 16px;background-color:#555;box-shadow:inset 0 0 6px rgba(0,0,0,.3);border-radius:10px;position:absolute;"></div></div><div id="box2" style="height: 16px;width: 200px;background-color:#F5F5F5;border-radius:10px;box-shadow:inset 0 0 6px rgba(0,0,0,0.3);position:relative;"> <div id="test2" style="height: 16px;width: 60px;background-color:#D62929;box-shadow:inset 0 0 6px rgba(0,0,0,.3);border-radius:10px;position:absolute;"></div></div><script>function scrollbar(obj,str){ obj.onmousedown = function(e){ e = e || event; var that = this; //x轴方向 if(str == 'x'){ var disX = e.clientX - this.offsetLeft; //否则为y轴方向 }else{ var disY = e.clientY - this.offsetTop; } document.onmousemove = function(e){ e = e || event; if(str == 'x'){ var L = e.clientX - disX; if(L < 0){L = 0;} var LMax = parseInt(obj.parentNode.style.width) - that.offsetWidth; if(L > LMax){L = LMax;} that.style.left = L + 'px'; }else{ var T = e.clientY - disY; if(T < 0){T = 0;} var TMax = parseInt(obj.parentNode.style.height) - that.offsetHeight; if(T > TMax){T = TMax;} that.style.top = T + 'px'; } } document.onmouseup = function(){ document.onmousemove = null; //释放全局捕获 if(obj.releaseCapture){obj.releaseCapture();} } //IE8-浏览器阻止默认行为 if(obj.setCapture){obj.setCapture();} //阻止默认行为 return false; } }scrollbar(test1);scrollbar(test2,'x')</script>应用
下面来介绍通过滚动条实现的几个应用
数字加减
通过移动滚动条来实现数字的加减。比例关系为：
滚动条已移动距离/滚动条可移动距离= 数字当前值/数字最大值
<div id="box" style="height: 16px;width: 200px;display:inline-block;background-color:#F5F5F5;border-radius:10px;box-shadow:inset 0 0 6px rgba(0,0,0,0.3);position:relative;"> <div id="test" style="height: 16px;width: 60px;background-color:#D62929;box-shadow:inset 0 0 6px rgba(0,0,0,.3);border-radius:10px;position:absolute;"></div></div><span id="result">0</span><script>function scrollbar(obj,str,max){ obj.onmousedown = function(e){ e = e || event; var that = this; //比例系数 var ratio; //x轴方向 if(str == 'x'){ var disX = e.clientX - this.offsetLeft; ratio = max/(this.parentNode.offsetWidth - this.offsetWidth); //否则为y轴方向 }else{ var disY = e.clientY - this.offsetTop; ratio =max/(this.parentNode.offsetHeight - this.offsetHeight); } document.onmousemove = function(e){ e = e || event; if(str == 'x'){ var L = e.clientX - disX; if(L < 0){L = 0;} var LMax = parseInt(obj.parentNode.style.width) - that.offsetWidth; if(L > LMax){L = LMax;} that.style.left = L + 'px'; result.innerHTML = Math.round(ratio * L); }else{ var T = e.clientY - disY; if(T < 0){T = 0;} var TMax = parseInt(obj.parentNode.style.height) - that.offsetHeight; if(T > TMax){T = TMax;} that.style.top = T + 'px'; result.innerHTML = Math.round(ratio * T); } } document.onmouseup = function(){ document.onmousemove = null; //释放全局捕获 if(obj.releaseCapture){obj.releaseCapture();} } //IE8-浏览器阻止默认行为 if(obj.setCapture){obj.setCapture();} //阻止默认行为 return false; } }scrollbar(test,'x',100);</script>元素尺寸
通过拖动滚动条来实现元素尺寸的变化，以改变元素宽度为例。比例关系为：
滚动条已移动距离/滚动条可移动距离= 元素当前宽度/元素最大宽度
<div id="box" style="height: 16px;width: 200px;display:inline-block;background-color:#F5F5F5;border-radius:10px;box-shadow:inset 0 0 6px rgba(0,0,0,0.3);position:relative;"> <div id="test" style="height: 16px;width: 60px;background-color:#D62929;box-shadow:inset 0 0 6px rgba(0,0,0,.3);border-radius:10px;position:absolute;"></div></div><span id="result" style="width: 1px;height: 50px;background-color:pink;display:inline-block;"></span><script>function scrollbar(obj,str,max){ obj.onmousedown = function(e){ e = e || event; var that = this; //比例系数 var ratio; //x轴方向 if(str == 'x'){ var disX = e.clientX - this.offsetLeft; ratio = max/(this.parentNode.offsetWidth - this.offsetWidth); //否则为y轴方向 }else{ var disY = e.clientY - this.offsetTop; ratio =max/(this.parentNode.offsetHeight - this.offsetHeight); } document.onmousemove = function(e){ e = e || event; if(str == 'x'){ var L = e.clientX - disX; if(L < 0){L = 0;} var LMax = parseInt(obj.parentNode.style.width) - that.offsetWidth; if(L > LMax){L = LMax;} that.style.left = L + 'px'; result.style.width = Math.round(ratio * L) + 'px'; }else{ var T = e.clientY - disY; if(T < 0){T = 0;} var TMax = parseInt(obj.parentNode.style.height) - that.offsetHeight; if(T > TMax){T = TMax;} that.style.top = T + 'px'; result.style.width = Math.round(ratio * T) + 'px'; } } document.onmouseup = function(){ document.onmousemove = null; //释放全局捕获 if(obj.releaseCapture){obj.releaseCapture();} } //IE8-浏览器阻止默认行为 if(obj.setCapture){obj.setCapture();} //阻止默认行为 return false; } }scrollbar(test,'x',100);</script>内容滚动
通过拖动滚动条来实现内容滚动，比例关系为：
滚动条已移动距离/滚动条可移动距离= 内容已移动距离/内容可移动距离
<div id="box" style="height: 200px;width: 16px;display:inline-block;background-color:#F5F5F5;border-radius:10px;box-shadow:inset 0 0 6px rgba(0,0,0,0.3);position:relative;vertical-align:middle;"> <div id="test" style="height: 60px;width: 16px;background-color:#D62929;box-shadow:inset 0 0 6px rgba(0,0,0,.3);border-radius:10px;position:absolute;"></div></div><span id="result" style="width: 100px;height: 200px;background-color:pink;display:inline-block;line-height:30px;vertical-align:middle;position:relative;overflow:hidden;"><div id="resultIn" style="position:absolute;top:0;">测试文字<br>测试文字<br>测试文字<br>测试文字<br>测试文字<br>测试文字<br>测试文字<br>测试文字<br>测试文字<br>测试文字<br>测试文字<br>测试文字<br></div></span><script>function scrollbar(obj,str){ var max = result.offsetHeight - resultIn.offsetHeight; obj.onmousedown = function(e){ e = e || event; var that = this; //比例系数 var ratio; //x轴方向 if(str == 'x'){ var disX = e.clientX - this.offsetLeft; ratio = max/(this.parentNode.offsetWidth - this.offsetWidth); //否则为y轴方向 }else{ var disY = e.clientY - this.offsetTop; ratio =max/(this.parentNode.offsetHeight - this.offsetHeight); } document.onmousemove = function(e){ e = e || event; if(str == 'x'){ var L = e.clientX - disX; if(L < 0){L = 0;} var LMax = parseInt(obj.parentNode.style.width) - that.offsetWidth; if(L > LMax){L = LMax;} that.style.left = L + 'px'; resultIn.style.top = Math.round(ratio * L) + 'px'; }else{ var T = e.clientY - disY; if(T < 0){T = 0;} var TMax = parseInt(obj.parentNode.style.height) - that.offsetHeight; if(T > TMax){T = TMax;} that.style.top = T + 'px'; resultIn.style.top = Math.round(ratio * T) + 'px'; } } document.onmouseup = function(){ document.onmousemove = null; //释放全局捕获 if(obj.releaseCapture){obj.releaseCapture();} } //IE8-浏览器阻止默认行为 if(obj.setCapture){obj.setCapture();} //阻止默认行为 return false; } }scrollbar(test,'y');</script>原标题：javascript动画系列第五篇——模拟滚动条
关键词：JavaScript
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