在requestAnimationFrame出现之前,我们一般都用setTimeout和setInterval,那么html5为什么新增一个requestAnimationFrame,他的出现是为了解决什么问题?
优势与特点:
1)requestAnimationFrame会把每一帧中的所有DOM操作集中起来,在一次重绘或回流中就完成,并且重绘或回流的时间间隔紧紧跟随浏览器的刷新频率
2)在隐藏或不可见的元素中,requestAnimationFrame将不会进行重绘或回流,这当然就意味着更少的CPU、GPU和内存使用量
3)requestAnimationFrame是由浏览器专门为动画提供的API,在运行时浏览器会自动优化方法的调用,并且如果页面不是激活状态下的话,动画会自动暂停,有效节省了CPU开销
一句话就是:这玩意性能高,不会卡屏,根据不同的浏览器自动调整帧率。如果看不懂或者不理解,也没有什么关系,这玩意跟浏览器渲染原理有关。我们先学会使用它!
如何使用requestAnimationFrame?
使用方式跟定时器setTimeout差不多,不同之处在于,他不需要设置时间间隔参数
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var timer = requestAnimationFrame( function(){ console.log( '定时器代码' ); } ); |
参数是一个回调函数,返回值是一个整数,用来表示定时器的编号.
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<!DOCTYPE html> < html lang = "en" > < head > < meta charset = "UTF-8" > < meta name = "viewport" content = "width=device-width, initial-scale=1.0" > < meta http-equiv = "X-UA-Compatible" content = "ie=edge" > < title >Document</ title > < script > window.onload = function(){ var aInput = document.querySelectorAll( "input" ), timer = null; aInput[0].onclick = function(){ timer = requestAnimationFrame( function say(){ console.log( 1 ); timer = requestAnimationFrame( say ); } ); }; aInput[1].onclick = function(){ cancelAnimationFrame( timer ); } } </ script > </ head > < body > < input type = "button" value = "开启" > < input type = "button" value = "关闭" > </ body > </ html > |
cancelAnimationFrame用来关闭定时器
这个方法需要处理兼容:
简单的兼容:
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window.requestAnimFrame = (function(){ return window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || function( callback ){ window.setTimeout(callback, 1000 / 60); }; })(); |
如果浏览器都不认识AnimationFrame,就用setTimeout兼容.
运用3种不同的定时器(setTimeout, setInterval, requestAnimationFrame)实现一个进度条的加载
一、setInterval方式:
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<!DOCTYPE html> < html lang = "en" > < head > < meta charset = "UTF-8" > < meta name = "viewport" content = "width=device-width, initial-scale=1.0" > < meta http-equiv = "X-UA-Compatible" content = "ie=edge" > < title >Document</ title > < style > div{ width:0px; height:40px; border-radius:20px; background:#09f; text-align:center; font:bold 30px/40px '微软雅黑'; color:white; } </ style > < script > window.onload = function(){ var oBtn = document.querySelector( "input" ), oBox = document.querySelector( "div" ), timer = null, curWidth = 0, getStyle = function( obj, name, value ){ if( obj.currentStyle ) { return obj.currentStyle[name]; }else { return getComputedStyle( obj, false )[name]; } }; oBtn.onclick = function(){ clearInterval( timer ); oBox.style.width = '0'; timer = setInterval( function(){ curWidth = parseInt( getStyle( oBox, 'width' ) ); if ( curWidth < 1000 ) { oBox.style.width = oBox.offsetWidth + 10 + 'px'; oBox.innerHTML = parseInt ( getStyle( oBox, 'width' ) ) / 10 + '%'; }else { clearInterval( timer ); } }, 1000 / 60 ); } } </script> </ head > < body > < div >0%</ div > < p >< input type = "button" value = "ready!Go" ></ p > </ body > </ html > |
二、setTimeout方式
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< script > window.onload = function(){ var oBtn = document.querySelector( "input" ), oBox = document.querySelector( "div" ), timer = null, curWidth = 0, getStyle = function( obj, name, value ){ if( obj.currentStyle ) { return obj.currentStyle[name]; }else { return getComputedStyle( obj, false )[name]; } }; oBtn.onclick = function(){ clearTimeout( timer ); oBox.style.width = '0'; timer = setTimeout( function go(){ curWidth = parseInt( getStyle( oBox, 'width' ) ); if ( curWidth < 1000 ) { oBox.style.width = oBox.offsetWidth + 10 + 'px'; oBox.innerHTML = parseInt ( getStyle( oBox, 'width' ) ) / 10 + '%'; timer = setTimeout ( go, 1000 / 60 ); }else { clearInterval( timer ); } }, 1000 / 60 ); } } </script> |
三、requestAnimationFrame方式
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<!DOCTYPE html> < html lang = "en" > < head > < meta charset = "UTF-8" > < meta name = "viewport" content = "width=device-width, initial-scale=1.0" > < meta http-equiv = "X-UA-Compatible" content = "ie=edge" > < title >Document</ title > < style > div{ width:0px; height:40px; border-radius:20px; background:#09f; text-align:center; font:bold 30px/40px '微软雅黑'; color:white; } </ style > < script > window.onload = function(){ var oBtn = document.querySelector( "input" ), oBox = document.querySelector( "div" ), timer = null, curWidth = 0, getStyle = function( obj, name, value ){ if( obj.currentStyle ) { return obj.currentStyle[name]; }else { return getComputedStyle( obj, false )[name]; } }; oBtn.onclick = function(){ cancelAnimationFrame( timer ); oBox.style.width = '0'; timer = requestAnimationFrame( function go(){ curWidth = parseInt( getStyle( oBox, 'width' ) ); if ( curWidth < 1000 ) { oBox.style.width = oBox.offsetWidth + 10 + 'px'; oBox.innerHTML = parseInt ( getStyle( oBox, 'width' ) ) / 10 + '%'; timer = requestAnimationFrame ( go ); }else { cancelAnimationFrame( timer ); } } ); } } </script> </ head > < body > < div >0%</ div > < p >< input type = "button" value = "ready!Go" ></ p > </ body > </ html > |
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