In-depth analysis of JavaScript and the movement of JS
This time I will bring you an in-depth JS movement in JavaScript. JS movement using JavaScriptWhat are the precautions?The following is a practical case, let’s take a look.
JS Movement Basics
Motion Framework
When starting movement, close the existing timer
Separate movement and stop (if/else)
1. Uniform motion
nbsp;HTML>
<meta>
<title>01-运动基础</title>
<style>
#div1 {width:200px; height:200px; background:red; position:absolute; top:50px; left:0px;} </style>
<script>
//定时器
var timer=null; function startMove() { var oDiv=document.getElementById('div1'); //为了保证只有一个定时器工作,把之前的定时器全关了
clearInterval(timer);
timer=setInterval(function (){ var speed=1; if(oDiv.offsetLeft>=300)
{
clearInterval(timer);
} else
{
oDiv.style.left=oDiv.offsetLeft+speed+'px';
}
}, 30);
} </script><input><div></div>
<!DOCTYPE HTML><html><head><meta charset="utf-8"><title>无标题文档</title><style>#div1 {width:150px; height:200px; background:green; position:absolute; left:-150px;}#div1 span {position:absolute; width:20px; height:60px; line-height:20px; background:blue; right:-20px; top:70px;}</style><script>window.onload=function (){ var oDiv=document.getElementById('div1');
oDiv.onmouseover=function () {
startMove(0);
};
oDiv.onmouseout=function () {
startMove(-150);
};
};var timer=null;function startMove(iTarget){ var oDiv=document.getElementById('div1');
clearInterval(timer);
timer=setInterval(function (){ //先初始化速度
var speed=0; //开始位置 > 终点位置:比方 起点:350 终点 50 要想到50这个位置,速度得为:-10;
//oDiv.offsetLeft : 起点位置
//iTarget终点位置
if(oDiv.offsetLeft>iTarget)
{
speed=-10;
} else
{
speed=10;
} //这个函数存在一个漏洞,如果oDiv.offsetLef 刚好t >=iTarget 定时器不会停止
if(oDiv.offsetLeft==iTarget)
{
clearInterval(timer);
} else
{
oDiv.style.left=oDiv.offsetLeft+speed+'px';
}
}, 30);
}</script></head><body><div id="div1">
<span>分享到</span></div></body></html>
3.Fade in and out
<!DOCTYPE html><html lang="en"><head>
<meta charset="UTF-8">
<title>03-淡入淡出</title>
<style>
div{
width: 200px;
height: 200px;
background-color: red;
opacity:0.3; //兼容chrome和ff
filtr:alpha(opacity:30);//兼容低版本的IE
} </style>
<script>
window.onload = function () { var oDiv = document.getElementsByTagName('div')[0];
oDiv.onmouseover = function () {
changeAlpha(100);
};
oDiv.onmouseout = function () {
changeAlpha(30);
}; var timer = null; var alpha = 30; function changeAlpha(isTarget) {
clearInterval(timer); var speed = 0;
timer = setInterval(function () { //注意这个速度判断要写在定时器里面
if (alpha < isTarget){
speed = 10;
}else {
speed = -10;
} if (alpha == isTarget){
clearInterval(timer);
}else {
alpha += speed;
oDiv.style.opacity = alpha/100;
oDiv.style.filter = 'alpha(opacity:'+alpha+')';
}
},30);
}
} </script></head><body><div></div></body></html>
3. Buffering movement
Gradually slows down and finally stops
The farther the distance, the greater the speed
The speed is determined by the distance
Speed = (target value - current value) / scaling factor
Math.ceil():向上取整 Math.ceil(3.41) 结果是4 ,Math.ceil(-9.8) 结果是 -9; Math.floor():向下取整 Math.floor(-0.9) 结果是 -1;
Example: Buffer menu
Bug: Speed rounding, decimals will cause trouble!!!
<html><head> <meta charset="utf-8"> <title>无标题文档</title> <style> *{ padding: 0; margin: 0; } #div1 {width:100px; height:100px; background:red; position:absolute; left:0; top:50px;} #div2 {width:1px; height:300px; position:absolute; left:300px; top:0; background:black;} </style> <script> function startMove() { var oDiv=document.getElementById('div1'); setInterval(function (){ var speed=(300-oDiv.offsetLeft)/10; //缓冲运动一定要取整,否则会出事的!!!! //Math.ceil():向上取整 Math.ceil(3.41) 结果是4 ,Math.ceil(-9.8) 结果是 -9; //Math.floor():向下取整 Math.floor(-0.9) 结果是 -1; //speed=Math.floor(speed); //速度大于0,向上取整,速度小于0,向下取整; speed=speed>0?Math.ceil(speed):Math.floor(speed); //速度不能为小数:速度里面有小数,导致oDiv.style.left的值带有小数,而oDiv.style.left会自动取整,导致他把小数抹掉了,导致误差!!! //故把速度向上取整,来避免此误差 oDiv.style.left=oDiv.offsetLeft+speed+'px'; document.title=oDiv.offsetLeft+','+speed; }, 30); } </script></head><body><input type="button" value="开始运动" onclick="startMove()" /><div id="div1"></div><div id="div2"></div></body></html>
Buffering movement one (there are compatibility issues on Chrome browser)
Buffering sidebar that follows page scrolling
Potential problem: When the target value is not an integer, it will If jitter occurs, just convert it to an integer! There may be an error of 0.5 pixels, which can be ignored!
suspended box on the right
Let’s learn some basic knowledge first
Get the scrolling distance of the browser scroll bar
1. When designing a page, the position of the fixed layer may often be used. This requires obtaining the coordinates of some html objects to set the coordinates of the target layer more flexibly. Attributes such as document.body.scrollTop may be used here, but the result of this attribute in an xhtml standard web page or, more simply, a page with a tag is 0. If this tag is not required, Then everything is normal, then how to get the coordinates of the body in the xhtml page? Of course there is a way - use document.documentElement to replace document.body, you can write like this
Example:
Get the scrolling distance of the browser scroll bar
var top = document.documentElement.scrollTop || document.body.scrollTop;
In JavaScript, || is a good thing. In addition to being used in if and other conditional judgments, it can also be used in variables Assignment. Then the above example is equivalent to the following example.
Example: var top = document.documentElement.scrollTop ? document.documentElement.scrollTop : document.body.scrollTop;
Writing like this can achieve good compatibility.
On the contrary, if no declaration is made, document.documentElement.scrollTop will be displayed as 0 instead.
document.body.clientWidth ==> BODY对象宽度document.body.clientHeight ==> BODY对象高度document.documentElement.clientWidth ==> 可见区域宽度document.documentElement.clientHeight ==> 可见区域高度
<html><head><meta charset="utf-8"><title>右侧悬浮窗</title><style>#div1 {width:100px; height:150px; background:red; position:absolute; right:0; bottom:0;}</style><script>window.onscroll=function (){ var oDiv=document.getElementById('div1'); var scrollTop=document.documentElement.scrollTop||document.body.scrollTop; //oDiv.style.top=document.documentElement.clientHeight-oDiv.offsetHeight+scrollTop+'px'; startMove(document.documentElement.clientHeight-oDiv.offsetHeight+scrollTop);};var timer=null;function startMove(iTarget){ var oDiv=document.getElementById('div1'); clearInterval(timer); timer=setInterval(function (){ var speed=(iTarget-oDiv.offsetTop)/4; speed=speed>0?Math.ceil(speed):Math.floor(speed); if(oDiv.offsetTop==iTarget) { clearInterval(timer); } else { oDiv.style.top=oDiv.offsetTop+speed+'px'; } }, 30);}</script></head><body style="height:2000px;"><div id="div1"></div></body></html>
Stop at a constant speed
//Absolute value,
Math.abs()
For example: (Math.abs(-6) ) and (Math.abs(6)) both result in 6. What he means is to change the value to have no sign, so it is all positive.
<html><head>
<meta charset="utf-8">
<title>无标题文档</title>
<style>
#div1 {width:100px; height:100px; background:red; position:absolute; left:600px; top:50px;} #div2 {width:1px; height:300px; position:absolute; left:300px; top:0; background:black;} #div3 {width:1px; height:300px; position:absolute; left:100px; top:0; background:black;} </style>
<script>
var timer=null; function startMove(iTarget) { var oDiv=document.getElementById('div1');
clearInterval(timer);
timer=setInterval(function (){ var speed=0; if(oDiv.offsetLeft<iTarget)
{
speed=10;
} else
{
speed=-10;
} //目标和物体之间的距离的绝对值小于等于速度,就算他达到目标了.
if(Math.abs(iTarget-oDiv.offsetLeft)<=Math.abs(speed))
{
clearInterval(timer); //目标和物体之间的有一小小的距离,计算误差导致的.
//让left直接等于目标点
oDiv.style.left=iTarget+'px';
} else
{
oDiv.style.left=oDiv.offsetLeft+speed+'px';
}
}, 30);
} </script></head><body><input type="button" value="到100" onclick="startMove(100)" /><input type="button" value="到300" onclick="startMove(300)" /><div id="div1"></div><div id="div2"></div><div id="div3"></div></body></html>
In-depth basic application of JavaScript
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