iscroll源码实现原理(一)
iscroll是移动端h5开发中为了实现原生滚动体验的一个库
他的主要特点是
- 接近原生的滚动体验(说明性能不差)
- 兼容性非常好(相信没哪个库敢说在H5上完美)
- 使用方便(只需要dom结构按照一定的规则)
- 功能强大(横向,纵向滚动,滚动条自定义,PC浏览器上的鼠标滚动都支持)
即便如此,当使用这个库的时候依然会踩到坑,比如配置没正确等,因此很有必要研读一下源码了解其使用原理,以便在遇到问题的时候能够快速解决,甚至构造自己的轻量级的iscroll组件
iscroll的实现核心
- 对touch事件的处理,包括开始,移动和结束
- css3或者降级(requestAnimationFrame,setTimeout等)来实现滚动动画
- 动画的物理效果，如加速,缓动,动量势能的计算等
iscroll源码
主要说明的几个重要文件iscroll
default文件夹下的文件
utils.js
utils的接口都为一些辅助方法，首先定义了requestAnimationFrame的兼容性方法
var rAF = window.requestAnimationFrame ||
window.webkitRequestAnimationFrame ||
window.mozRequestAnimationFrame ||
window.oRequestAnimationFrame ||
window.msRequestAnimationFrame ||
function (callback) { window.setTimeout(callback, 1000 / 60); };
定义css的transform前缀判断来实现兼容
var _elementStyle = document.createElement('div').style;
var _vendor = (function () {
var vendors = ['t', 'webkitT', 'MozT', 'msT', 'OT'],
transform,
i = 0,
l = vendors.length;
for ( ; i < l; i++ ) {
transform = vendors[i] + 'ransform';
if ( transform in _elementStyle ) return vendors[i].substr(0, vendors[i].length-1);
}
return false;
})();
function _prefixStyle (style) {
if ( _vendor === false ) return false;
if ( _vendor === '' ) return style;
return _vendor + style.charAt(0).toUpperCase() + style.substr(1);
}
获取当前时间,注意后面的me都为utils对象本身
me.getTime = Date.now || function getTime () { return new Date().getTime(); };
潜复制对象属性
me.extend = function (target, obj) {
for ( var i in obj ) {
target[i] = obj[i];
}
};
事件的注册与取消
me.addEvent = function (el, type, fn, capture) {
el.addEventListener(type, fn, !!capture);
};
me.removeEvent = function (el, type, fn, capture) {
el.removeEventListener(type, fn, !!capture);
};
定义势能函数,这里会根据输入参数设置滚动的加速度
me.momentum = function (current, start, time, lowerMargin, wrapperSize, deceleration) {
var distance = current - start,
speed = Math.abs(distance) / time,
destination,
duration;
deceleration = deceleration === undefined ? 0.0006 : deceleration;
destination = current + ( speed * speed ) / ( 2 * deceleration ) * ( distance < 0 ? -1 : 1 );
duration = speed / deceleration;
if ( destination < lowerMargin ) {
destination = wrapperSize ? lowerMargin - ( wrapperSize / 2.5 * ( speed / 8 ) ) : lowerMargin;
distance = Math.abs(destination - current);
duration = distance / speed;
} else if ( destination > 0 ) {
destination = wrapperSize ? wrapperSize / 2.5 * ( speed / 8 ) : 0;
distance = Math.abs(current) + destination;
duration = distance / speed;
}
return {
destination: Math.round(destination),
duration: duration
};
};
给utils定义一些bool值属性，用来检测浏览器是否支持某些特性
me.extend(me, {
hasTransform: _transform !== false,//
hasPerspective: _prefixStyle('perspective') in _elementStyle,
hasTouch: 'ontouchstart' in window,
hasPointer: window.PointerEvent || window.MSPointerEvent, // IE10 is prefixed
hasTransition: _prefixStyle('transition') in _elementStyle
});
筛选某些安卓版本,appVersion中有android字符没有chrome字符应该是比较旧的版本,应该是会填坑用的
me.isBadAndroid = /Android /.test(window.navigator.appVersion) && !(/Chrome\/\d/.test(window.navigator.appVersion));
设置transform的css3过渡属性
me.extend(me.style = {}, {
transform: _transform,
transitionTimingFunction: _prefixStyle('transitionTimingFunction'),
transitionDuration: _prefixStyle('transitionDuration'),
transitionDelay: _prefixStyle('transitionDelay'),
transformOrigin: _prefixStyle('transformOrigin')
});
样式类的操作
me.hasClass = function (e, c) {
var re = new RegExp("(^|\\s)" + c + "(\\s|$)");
return re.test(e.className);
};
me.addClass = function (e, c) {
if ( me.hasClass(e, c) ) {
return;
}
var newclass = e.className.split(' ');
newclass.push(c);
e.className = newclass.join(' ');
};
me.removeClass = function (e, c) {
if ( !me.hasClass(e, c) ) {
return;
}
var re = new RegExp("(^|\\s)" + c + "(\\s|$)", 'g');
e.className = e.className.replace(re, ' ');
};
获取某个元素相对于根元素的偏移offset,后面会用到
me.offset = function (el) {
var left = -el.offsetLeft,
top = -el.offsetTop;
// jshint -W084
while (el = el.offsetParent) {
left -= el.offsetLeft;
top -= el.offsetTop;
}
// jshint +W084
return {
left: left,
top: top
};
};
iscroll默认会阻止默认行为,但一些元素如果阻止默认行为会有很大影响,如输入框input元素等,因此把这些设置为例外,后面会用到
me.preventDefaultException = function (el, exceptions) {
for ( var i in exceptions ) {
if ( exceptions[i].test(el[i]) ) {
return true;
}
}
return false;
};
定义事件的类似枚举类型
me.extend(me.eventType = {}, {
touchstart: 1,
touchmove: 1,
touchend: 1,
mousedown: 2,
mousemove: 2,
mouseup: 2,
pointerdown: 3,
pointermove: 3,
pointerup: 3,
MSPointerDown: 3,
MSPointerMove: 3,
MSPointerUp: 3
});
定义动画的擦除ease函数
me.extend(me.ease = {}, {
quadratic: {
style: 'cubic-bezier(0.25, 0.46, 0.45, 0.94)',
fn: function (k) {
return k * ( 2 - k );
}
},
circular: {
style: 'cubic-bezier(0.1, 0.57, 0.1, 1)', // Not properly "circular" but this looks better, it should be (0.075, 0.82, 0.165, 1)
fn: function (k) {
return Math.sqrt( 1 - ( --k * k ) );
}
},
back: {
style: 'cubic-bezier(0.175, 0.885, 0.32, 1.275)',
fn: function (k) {
var b = 4;
return ( k = k - 1 ) * k * ( ( b + 1 ) * k + b ) + 1;
}
},
bounce: {
style: '',
fn: function (k) {
if ( ( k /= 1 ) < ( 1 / 2.75 ) ) {
return 7.5625 * k * k;
} else if ( k < ( 2 / 2.75 ) ) {
return 7.5625 * ( k -= ( 1.5 / 2.75 ) ) * k + 0.75;
} else if ( k < ( 2.5 / 2.75 ) ) {
return 7.5625 * ( k -= ( 2.25 / 2.75 ) ) * k + 0.9375;
} else {
return 7.5625 * ( k -= ( 2.625 / 2.75 ) ) * k + 0.984375;
}
}
},
elastic: {
style: '',
fn: function (k) {
var f = 0.22,
e = 0.4;
if ( k === 0 ) { return 0; }
if ( k == 1 ) { return 1; }
return ( e * Math.pow( 2, - 10 * k ) * Math.sin( ( k - f / 4 ) * ( 2 * Math.PI ) / f ) + 1 );
}
}
});
自定义tap事件,用户可以用tap事件来模拟click,同时消除300ms延迟,后面细说
me.tap = function (e, eventName) {
var ev = document.createEvent('Event');
ev.initEvent(eventName, true, true);
ev.pageX = e.pageX;
ev.pageY = e.pageY;
e.target.dispatchEvent(ev);
};
重写原生的click事件,除了一些特殊标签,后面会用到
me.click = function (e) {
var target = e.target,
ev;
if ( !(/(SELECT|INPUT|TEXTAREA)/i).test(target.tagName) ) {
ev = document.createEvent('MouseEvents');
ev.initMouseEvent('click', true, true, e.view, 1,
target.screenX, target.screenY, target.clientX, target.clientY,
e.ctrlKey, e.altKey, e.shiftKey, e.metaKey,
0, null);
ev._constructed = true;
target.dispatchEvent(ev);
}
};