权值等级的定义
第一等:代表内联样式,如: style=””,权值为1000。
第二等:代表ID选择器,如:#content,权值为100。
第三等:代表类,伪类和属性选择器,如.content,权值为10。
第四等:代表类型选择器和伪元素选择器,如div p,权值为1。
Ps:通用选择器(*),子选择器(>)和相邻同胞选择器(+)并不在这四个等级中,所以他们的权值都为0,!important 优先级最高,万不得已的情况下才用。
权重计算
#content div#main-content h2=2*100+2*1=202 #content #main-content>h2=2*100+1=201 body #content div[id="main-content"] h2=1*100+1*10+3*1=113 #main-content div.paragraph h2=1*100+1*10+2*1=112 #main-content [class="paragraph"] h2=1*100+1*10+1*1=111 div#main-content div.paragraph h2.first=1*100+2*10+3*1=123
优先规则
权值大的样式会覆盖权值小的样式,上面例子的样式会采用权值最大201的样式,当你乱用!important,特别是后期修改样式的时候,是不是有种心力憔悴电费感觉?
当css前后样式项的权值一样,后面的样式会覆盖前面的样式。
Css 概念
命名风格规范
1 css文件命名:统一为小写的英文字母(尽量少用拼音),如:index.css。
当名字需要组合拼写时,可以在单词间加中杠线(不要用下划线:容易写错)。如:member-report.css。(推荐)
或者统一为驼峰式拼写。如:MemberReport.css (项目启动前统一风格)。
2 样式名(html的class名):在让人看懂的前提下,尽量语义化或简写。尽量少用拼音,和无语义的缩写 .bt .bd 等; 风格可以统一为小写字母,如:content。当名字需要组合时,可以采用css文件名的规范。
样式的继承
文本样式
color,font-family, font-size, font-style, font-variant, font-weight, font, letter-spacing, line-height,text-align, text-indent, texttransform,word-spacing
列表相关属性
list-style-image, list-style-position, list-style-type, list-style,
像素化 css
渲染
就是浏览器把HTML代码以css定义的规则显示在浏览器窗口的过程
浏览器对页面呈现的处理流程
回流
当页面的布局发生变化时,浏览器会回过头来重新渲染,这就是页面为什么会慢的一个原因,当一个点的变 化影响了布局,这就会使得要倒回去重新渲染,这个倒回去的过程称为 reflow(回流)。
当页面布局和几何属性改变时就需要回流。下述情况会发生浏览器回流
var s = document.body.style; s.padding = "2px"; // 回流+重绘 s.border = "1px solid red"; // 再一次 回流+重绘 s.color = "blue"; // 再一次重绘 s.backgroundColor = "#ccc"; // 再一次 重绘 s.fontSize = "14px"; // 再一次 回流+重绘 // 添加node,再一次 回流+重绘 document.body.appendChild(document.createTextNode('abc!')); 回流比重绘的代价要更高,回流的花销跟render tree有多少节点需要重新构建有关系,假设你直接操作body,比如在body最前面插入1个元素,会导致整个render tree回流,这样代价当然会比较高,但如果是指body后面插入1个元素,则不会影响前面元素的回流。
reflow问题也是可以优化的,减少reflow是很有必要的,比如给图片设定好宽度和高度,这样就可以把图片的占位面积预定好。
重绘
一些元素需要更新属性,而这些属性只是影响元素的外观,风格(景颜色,文字颜色,边框颜色)而不会影响布局,浏览器就会repaint。repaint的速度明显比reflow的速度快。
为了帮助小伙伴们更好的学习WEB前端,技术学派整理了WEB前端的相关学习视频及学习路线图。
关注“技术学派”后,评论转发文章,私信回复:WEB前端
天遇到个来咨询利用原生的JS代码来修改HTML代码的的童鞋,耐心的给这个童鞋做了解答后,然后整理了一下测试代码,写成文章记录一下,方便以后有同需求的站长们。
HTML原始代码
<form action="" method="post" class="form"> <input id="mm" type="text" > <input id="mochu" type="text" onclick="act(this.value)" /> <input id="mc" type="text" > </form>
利用JS代码将以上HTML代中的 id 为 mochu 的 input 中的 cnclick 属性去掉
<input id="mochu" type="text" onclick="act(this.value)" />
换成
<input id="mochu" type="text" />
利用 JS中dom对象的 outerHTML 属性,可以轻松的解决这个问题
outerHTML:设置或获取对象及其内容的 HTML 形式
例:JS获取元表本身的HTML代码
代码:
<!DOCTYPE html>
<html>
<head>
</head>
<body>
<form action="" method="post" class="form">
<input id="mm" type="text" value="飞鸟慕鱼博客" >
<input id="mochu" type="text" onclick="act(this.value)" value="http://www.feiniaomy.com" />
<input id="mc" type="text" >
</form>
<script>
var html = document.getElementById('mochu').outerHTML;
console.log(html);
</script>
</body>
</html>
打印结果:
例:js修改指定元素的本身的HTML代码
通上面的例子,可以知道 outerHTML 属性可以获取到元素本身的HTML代码,既然可以获取也能设置或修改元素本身的代码
代码:
<!DOCTYPE html> <html> <head> </head> <body> <form action="" method="post" class="form"> <input id="mm" type="text" value="飞鸟慕鱼博客" > <input id="mochu" type="text" onclick="act(this.value)"/> <input id="mc" type="text" > </form> <script> var html = document.getElementById('mochu').outerHTML = '<input id="mochu" type="text" value="http://www.feiniaomy.com" />'; </script> </body> </html>
运行结果如图所示
以下是与 outerHTML 功能相似的属性,下一篇文章会详细说明一下他们的作用与区别
innerHTML:设置或获取对象起始标签和结束标签之间的内容。
innerText:设置或获取位于对象起始和结束标签内的文本
outerHTML:设置或获取对象及其内容的 HTML 形式
outerText:设置或获取对象的文本
言:每当过节的时候,女朋友就抱怨我总是忘记给她买花,说程序不懂浪漫,这不我准备了几款爱心动画特效,打算当面向她表达一下。
寓意:告白无须多么华丽的语言,一颗颗小的爱心汇聚成一颗真心,让你的另一半感受到浓浓的爱意。
代码难度系数★★★
新建index.html,复制以下代码保存在浏览器中打开即可。
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>canvas 心</title>
<style>
html, body {
height: 100%;
padding: 0;
margin: 0;
background: #000;
}
canvas {
position: absolute;
width: 100%;
height: 100%;
}</style>
</head>
<body>
<canvas id="pinkboard"></canvas>
<script>
/*
* Settings
*/
var settings = {
particles: {
length: 500, // maximum amount of particles
duration: 2, // particle duration in sec
velocity: 100, // particle velocity in pixels/sec
effect: -0.75, // play with this for a nice effect
size: 30, // particle size in pixels
},
};
/*
* RequestAnimationFrame polyfill by Erik M?ller
*/
(function(){var b=0;var c=["ms","moz","webkit","o"];for(var a=0;a<c.length&&!window.requestAnimationFrame;++a){window.requestAnimationFrame=window[c[a]+"RequestAnimationFrame"];window.cancelAnimationFrame=window[c[a]+"CancelAnimationFrame"]||window[c[a]+"CancelRequestAnimationFrame"]}if(!window.requestAnimationFrame){window.requestAnimationFrame=function(h,e){var d=new Date().getTime();var f=Math.max(0,16-(d-b));var g=window.setTimeout(function(){h(d+f)},f);b=d+f;return g}}if(!window.cancelAnimationFrame){window.cancelAnimationFrame=function(d){clearTimeout(d)}}}());
/*
* Point class
*/
var Point = (function() {
function Point(x, y) {
this.x = (typeof x !== 'undefined') ? x : 0;
this.y = (typeof y !== 'undefined') ? y : 0;
}
Point.prototype.clone = function() {
return new Point(this.x, this.y);
};
Point.prototype.length = function(length) {
if (typeof length == 'undefined')
return Math.sqrt(this.x * this.x + this.y * this.y);
this.normalize();
this.x *= length;
this.y *= length;
return this;
};
Point.prototype.normalize = function() {
var length = this.length();
this.x /= length;
this.y /= length;
return this;
};
return Point;
})();
/*
* Particle class
*/
var Particle = (function() {
function Particle() {
this.position = new Point();
this.velocity = new Point();
this.acceleration = new Point();
this.age = 0;
}
Particle.prototype.initialize = function(x, y, dx, dy) {
this.position.x = x;
this.position.y = y;
this.velocity.x = dx;
this.velocity.y = dy;
this.acceleration.x = dx * settings.particles.effect;
this.acceleration.y = dy * settings.particles.effect;
this.age = 0;
};
Particle.prototype.update = function(deltaTime) {
this.position.x += this.velocity.x * deltaTime;
this.position.y += this.velocity.y * deltaTime;
this.velocity.x += this.acceleration.x * deltaTime;
this.velocity.y += this.acceleration.y * deltaTime;
this.age += deltaTime;
};
Particle.prototype.draw = function(context, image) {
function ease(t) {
return (--t) * t * t + 1;
}
var size = image.width * ease(this.age / settings.particles.duration);
context.globalAlpha = 1 - this.age / settings.particles.duration;
context.drawImage(image, this.position.x - size / 2, this.position.y - size / 2, size, size);
};
return Particle;
})();
/*
* ParticlePool class
*/
var ParticlePool = (function() {
var particles,
firstActive = 0,
firstFree = 0,
duration = settings.particles.duration;
function ParticlePool(length) {
// create and populate particle pool
particles = new Array(length);
for (var i = 0; i < particles.length; i++)
particles[i] = new Particle();
}
ParticlePool.prototype.add = function(x, y, dx, dy) {
particles[firstFree].initialize(x, y, dx, dy);
// handle circular queue
firstFree++;
if (firstFree == particles.length) firstFree = 0;
if (firstActive == firstFree ) firstActive++;
if (firstActive == particles.length) firstActive = 0;
};
ParticlePool.prototype.update = function(deltaTime) {
var i;
// update active particles
if (firstActive < firstFree) {
for (i = firstActive; i < firstFree; i++)
particles[i].update(deltaTime);
}
if (firstFree < firstActive) {
for (i = firstActive; i < particles.length; i++)
particles[i].update(deltaTime);
for (i = 0; i < firstFree; i++)
particles[i].update(deltaTime);
}
// remove inactive particles
while (particles[firstActive].age >= duration && firstActive != firstFree) {
firstActive++;
if (firstActive == particles.length) firstActive = 0;
}
};
ParticlePool.prototype.draw = function(context, image) {
// draw active particles
if (firstActive < firstFree) {
for (i = firstActive; i < firstFree; i++)
particles[i].draw(context, image);
}
if (firstFree < firstActive) {
for (i = firstActive; i < particles.length; i++)
particles[i].draw(context, image);
for (i = 0; i < firstFree; i++)
particles[i].draw(context, image);
}
};
return ParticlePool;
})();
/*
* Putting it all together
*/
(function(canvas) {
var context = canvas.getContext('2d'),
particles = new ParticlePool(settings.particles.length),
particleRate = settings.particles.length / settings.particles.duration, // particles/sec
time;
// get point on heart with -PI <= t <= PI
function pointOnHeart(t) {
return new Point(
160 * Math.pow(Math.sin(t), 3),
130 * Math.cos(t) - 50 * Math.cos(2 * t) - 20 * Math.cos(3 * t) - 10 * Math.cos(4 * t) + 25
);
}
// creating the particle image using a dummy canvas
var image = (function() {
var canvas = document.createElement('canvas'),
context = canvas.getContext('2d');
canvas.width = settings.particles.size;
canvas.height = settings.particles.size;
// helper function to create the path
function to(t) {
var point = pointOnHeart(t);
point.x = settings.particles.size / 2 + point.x * settings.particles.size / 350;
point.y = settings.particles.size / 2 - point.y * settings.particles.size / 350;
return point;
}
// create the path
context.beginPath();
var t = -Math.PI;
var point = to(t);
context.moveTo(point.x, point.y);
while (t < Math.PI) {
t += 0.01; // baby steps!
point = to(t);
context.lineTo(point.x, point.y);
}
context.closePath();
// create the fill
context.fillStyle = '#ea80b0';
context.fill();
// create the image
var image = new Image();
image.src = canvas.toDataURL();
return image;
})();
// render that thing!
function render() {
// next animation frame
requestAnimationFrame(render);
// update time
var newTime = new Date().getTime() / 1000,
deltaTime = newTime - (time || newTime);
time = newTime;
// clear canvas
context.clearRect(0, 0, canvas.width, canvas.height);
// create new particles
var amount = particleRate * deltaTime;
for (var i = 0; i < amount; i++) {
var pos = pointOnHeart(Math.PI - 2 * Math.PI * Math.random());
var dir = pos.clone().length(settings.particles.velocity);
particles.add(canvas.width / 2 + pos.x, canvas.height / 2 - pos.y, dir.x, -dir.y);
}
// update and draw particles
particles.update(deltaTime);
particles.draw(context, image);
}
// handle (re-)sizing of the canvas
function onResize() {
canvas.width = canvas.clientWidth;
canvas.height = canvas.clientHeight;
}
window.onresize = onResize;
// delay rendering bootstrap
setTimeout(function() {
onResize();
render();
}, 10);
})(document.getElementById('pinkboard'));</script>
</body>
</html>
寓意:将想说的话打开一颗颗的爱心气球上,随着气球不断的升空,让整个氛围可更加地缠绵,看到此处可以有感动的泪水。
代码难度系数★★★
新建index.html,复制以下代码保存在浏览器中打开即可。
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>情人节快乐:)</title>
<style>
canvas {
position: absolute;
top: 0;
left: 0;
}</style>
</head>
<body>
<canvas id=c></canvas>
<script>
var w = c.width = window.innerWidth,
h = c.height = window.innerHeight,
ctx = c.getContext( '2d' ),
opts = {
phrases: [ "Don't die\nit's not hard", "You're the Best", "Every day,\nYou're beautiful", "Every occasion,\nYou're clever", "A world without You?\nNah", "Keep kicking ass", "You're better than them,\nwhoever they are", "You're just amazing", "You are,\ntherefore I am", "Nothing better than You \ncould have happened to the world" ],
balloons: 10,
baseVelY: -1,
addedVelY: -1,
baseVelX: -.25,
addedVelX: .5,
baseSize: 20,
addedSize: 10,
baseSizeAdder: 2,
addedSizeAdder: 2,
baseIncrementer: .01,
addedIncrementer: .03,
baseHue: -10,
addedHue: 30,
font: '15px Verdana'
},
cycle = 0,
balloons = [];
ctx.font = opts.font;
function Balloon(){
this.reset();
}
Balloon.prototype.reset = function(){
this.size = opts.baseSize + opts.addedSize * Math.random();
this.sizeAdder = opts.baseSizeAdder + opts.addedSizeAdder * Math.random();
this.incrementer = opts.baseIncrementer + opts.addedIncrementer * Math.random();
this.tick = 0;
this.x = Math.random() * w;
this.y = h + this.size;
this.vx = opts.baseVelX + opts.addedVelX * Math.random();
this.vy = opts.baseVelY + opts.addedVelY * Math.random();
this.color = 'hsla(hue,70%,60%,.8)'.replace( 'hue', opts.baseHue + opts.addedHue * Math.random() );
this.phrase = opts.phrases[ ++cycle % opts.phrases.length ].split( '\n' );
this.lengths = [];
for( var i = 0; i < this.phrase.length; ++i )
this.lengths.push( -ctx.measureText( this.phrase[ i ] ).width / 2 );
}
Balloon.prototype.step = function(){
this.tick += this.incrementer;
this.x += this.vx;
this.y += this.vy;
var size = this.size + this.sizeAdder * Math.sin( this.tick );
ctx.lineWidth = size / 40;
ctx.strokeStyle = '#eee';
ctx.beginPath();
ctx.moveTo( this.x, this.y - 2 );
ctx.lineTo( this.x, this.y + size );
ctx.stroke();
ctx.fillStyle = this.color;
ctx.translate( this.x, this.y );
ctx.rotate( Math.PI / 4 );
//ctx.fillRect( -size / 2, -size / 2, size / 2, size / 2 );
ctx.beginPath();
ctx.moveTo( 0, 0 );
ctx.arc( -size / 2, -size / 2 + size / 4, size / 4, Math.PI / 2, Math.PI * 3 / 2 );
ctx.arc( -size / 2 + size / 4, -size / 2, size / 4, Math.PI, Math.PI * 2 );
ctx.lineTo( 0, 0 );
ctx.fill();
ctx.rotate( -Math.PI / 4 );
ctx.translate( -this.x, -this.y );
ctx.translate( this.x, this.y + size + 15 );
ctx.scale( size / this.size, size / this.size );
ctx.fillStyle = '#eee';
for( var i = 0; i < this.phrase.length; ++i )
ctx.fillText( this.phrase[ i ], this.lengths[ i ], i * 15 );
ctx.scale( this.size / size, this.size / size );
ctx.translate( -this.x, -( this.y + size + 15 ) );
if( this.y < -size * 3 )
this.reset();
}
function anim(){
window.requestAnimationFrame( anim );
ctx.fillStyle = '#222';
ctx.fillRect( 0, 0, w, h );
if( balloons.length < opts.balloons && Math.random() < .01 )
balloons.push( new Balloon );
for( var i = 0; i < balloons.length; ++i )
balloons[ i ].step();
}
anim();</script>
</body>
</html>
寓意:天空中下起了爱心雨,衬托的房间变得温暖,也让整个场景都变得温馨无比,想必此时可以有一个大大的拥抱。
代码难度系数★★★
代码有image、js和html,所以不好贴出来,有需要的朋友直接问我要吧。
总结:程序员的工作本身就很枯燥,特定找了几个好看的特效拿出来和大家分享,希望大家能够快乐每一天,上述代码亲测可用,欢迎点赞收藏。
《完》
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