是新近的firefox浏览器中支持overflow, underflow这两个事件,当某一元素的大小超出父元素的显示范围就会触发overflow事件,如果从超出显示再变回不超出的状态则触发underflow事件.
<!DOCTYPE HTML> <html> <head> <meta charset="UTF-8"> <title>测试用例 by 司徒正美</title> </head> <body > <div id="wrapper"> <div id="child"></div> </div> <br/> <label><input type="checkbox" id="toggle" checked/> Overflow</label> <style> #wrapper { width: 300px; height: 300px; background: blue; overflow: hidden; } #child { width: 200px; height: 200px; background: yellow; } </style> <script> var wrapper = document.getElementById("wrapper"), child = document.getElementById("child"), toggle = document.getElementById("toggle"); wrapper.addEventListener("overflow", function(event) { console.log(event); }, false); wrapper.addEventListener("underflow", function(event) { console.log(event); }, false); toggle.addEventListener("change", function(event) { if (event.target.checked) { child.style.width = "400px"; child.style.height = "400px"; } else { child.style.width = "200px"; child.style.height = "200px"; } }, false); </script> </body> </html>测试用例 by 司徒正美
运行代码
如果是webkit系统的浏览器,则用overflowchanged这个事件代替
<!DOCTYPE HTML> <html> <head> <meta charset="UTF-8"> <title>测试用例 by 司徒正美</title> </head> <body > <div id="wrapper"> <div id="child"></div> </div> <br/> <label><input type="checkbox" id="toggle" checked/> Overflow</label> <style> #wrapper { width: 300px; height: 300px; background: blue; overflow: hidden; } #child { width: 200px; height: 200px; background: yellow; } </style> <script> var wrapper = document.getElementById("wrapper"), child = document.getElementById("child"), toggle = document.getElementById("toggle"); wrapper.addEventListener("overflowchanged", function(event) { var overflow = event.verticalOverflow || event.horizontalOverflow var type = overflow ? "overflow" : "underflow" delete event.type event.type = type console.log(event) }, false); toggle.addEventListener("change", function(event) { if (event.target.checked) { child.style.width = "400px"; child.style.height = "400px"; } else { child.style.width = "200px"; child.style.height = "200px"; } }, false); </script> </body> </html>运行代码
对于不支持的浏览器,那只能轮询判定是否存在滚动条了,可以看