我正在尝试使用
纯 JavaScript 为div
制作淡出效果。
这是我目前使用的:
//Imagine I want to fadeOut an element with id = "target"
function fadeOutEffect()
{
var fadeTarget = document.getElementById("target");
var fadeEffect = setInterval(function() {
if (fadeTarget.style.opacity < 0.1)
{
clearInterval(fadeEffect);
}
else
{
fadeTarget.style.opacity -= 0.1;
}
}, 200);
}
div 应该平滑淡出,但它立即消失。
怎么了?我该如何解决?
最初当没有设置不透明度时,该值将是一个空字符串,这将导致您的算术失败。也就是说,
"" < 0.1 == true
并且您的代码进入clearInterval
分支。
您可以将其默认为 1,它会起作用。
function fadeOutEffect() {
var fadeTarget = document.getElementById("target");
var fadeEffect = setInterval(function () {
if (!fadeTarget.style.opacity) {
fadeTarget.style.opacity = 1;
}
if (fadeTarget.style.opacity > 0) {
fadeTarget.style.opacity -= 0.1;
} else {
clearInterval(fadeEffect);
}
}, 200);
}
document.getElementById("target").addEventListener('click', fadeOutEffect);
#target {
height: 100px;
background-color: red;
}
<div id="target">Click to fade</div>
在进行算术和比较时,空字符串似乎被 JavaScript 视为 0(即使在 CSS 中它将空字符串视为完全不透明)
> '' < 0.1
> true
> '' > 0.1
> false
> '' - 0.1
> -0.1
更简单的方法 我们现在可以使用 CSS transitions 以更少的代码实现淡出
const target = document.getElementById("target");
target.addEventListener('click', () => target.style.opacity = '0');
// If you want to remove it from the page after the fadeout
target.addEventListener('transitionend', () => target.remove());
#target {
height: 100px;
background-color: red;
transition: opacity 1s;
}
<p>Some text before<p>
<div id="target">Click to fade</div>
<p>Some text after</p>
就在今天早上,我在http://vanilla-js.com找到了这段代码,非常简单、紧凑、快速:
var s = document.getElementById('thing').style;
s.opacity = 1;
(function fade(){(s.opacity-=.1)<0?s.display="none":setTimeout(fade,40)})();
您可以通过改变
setTimeOut
函数中的第二个参数来改变淡入淡出的速度。
var s = document.getElementById('thing').style;
s.opacity = 1;
(function fade(){(s.opacity-=.1)<0?s.display="none":setTimeout(fade,40)})();
#thing {
background: red;
line-height: 40px;
}
<div id="thing">I will fade...</div>
看起来你可以用另一种方式来做(我可能错了)。
event.target.style.transition = '0.8s';
event.target.style.opacity = 0;
你可以使用 CSS transition 属性而不是在 javascript 中做 vai timer。与您正在做的事情相比,这更注重绩效。
检查
除了已接受的答案外,我们现在还有 WAAPI,它基本上将动画 API 添加到 JavaScript。
例如,
/**
* @returns {Object}
*/
function defaultFadeConfig() {
return {
easing: 'linear',
iterations: 1,
direction: 'normal',
fill: 'forwards',
delay: 0,
endDelay: 0
}
}
/**
* @param {HTMLElement} el
* @param {number} durationInMs
* @param {Object} config
* @returns {Promise}
*/
async function fadeOut(el, durationInMs, config = defaultFadeConfig()) {
return new Promise((resolve, reject) => {
const animation = el.animate([
{ opacity: '1' },
{ opacity: '0', offset: 0.5 },
{ opacity: '0', offset: 1 }
], {duration: durationInMs, ...config});
animation.onfinish = () => resolve();
})
}
/**
* @param {HTMLElement} el
* @param {number} durationInMs
* @param {Object} config
* @returns {Promise}
*/
async function fadeIn(el, durationInMs, config = defaultFadeConfig()) {
return new Promise((resolve) => {
const animation = el.animate([
{ opacity: '0' },
{ opacity: '0.5', offset: 0.5 },
{ opacity: '1', offset: 1 }
], {duration: durationInMs, ...config});
animation.onfinish = () => resolve();
});
}
window.addEventListener('load', async ()=> {
const el = document.getElementById('el1');
for(const ipsum of "Neque porro quisquam est qui dolorem ipsum quia dolor \uD83D\uDE00".split(' ')) {
await fadeOut(el, 1000);
el.innerText = ipsum;
await fadeIn(el, 2000);
}
});
.text-center {
text-align: center;
}
<h1 id="el1" class="text-center">...</h1>
function fadeOutEffect() {
var fadeTarget = document.getElementById("target");
var fadeEffect = setInterval(function () {
if (!fadeTarget.style.opacity) {
fadeTarget.style.opacity = 1;
}
if (fadeTarget.style.opacity > 0) {
fadeTarget.style.opacity -= 0.1;
} else {
clearInterval(fadeEffect);
}
}, 200);
}
document.getElementById("target").addEventListener('click', fadeOutEffect);
#target {
height: 100px;
background-color: red;
}
<div id="target">Click to fade</div>
我的解决方案
function fadeOut(selector, timeInterval, callback = null) {
var fadeTarget = document.querySelector(selector);
let time = timeInterval / 1000;
fadeTarget.style.transition = time + 's';
fadeTarget.style.opacity = 0;
var fadeEffect = setInterval(function() {
if (fadeTarget.style.opacity <= 0)
{
clearInterval(fadeEffect);
if (typeof (callback) === 'function') {
callback();
}
}
}, timeInterval);
}
虽然这个和其他 SO 线程中的大多数解决方案都有效,但这是我的两分钱。如果你只想依赖纯 JS 那么这应该可以解决问题:
function fadeOutEle(el) {
el.style.opacity = 1;
(function fade() {
if ((el.style.opacity -= .009) < 0) {
el.style.display = "none";
} else {
requestAnimationFrame(fade);
}
})();
};
这里的关键是
el.style.opacity -= .009
,它提供了很酷的淡出效果。保持低于 1/2 秒(在本例中为 0.009),以便在元素隐藏之前效果可见。
对于最具交互性的用法,考虑将给定的(基于)函数集成到添加的参数中:
function fadeOut(yourElementId, wishedDuration) {
const yourElementPath = document.getElementById(yourElementId);
const fadeTarget = yourElementPath;
const fadeEffect = setInterval(function () {
if (!fadeTarget.style.opacity) {
fadeTarget.style.opacity = 1;
}
if (fadeTarget.style.opacity > 0) {
fadeTarget.style.opacity -= .01; //set your own value here
} else {
clearInterval(fadeEffect);
}
}, wishedDuration);
}
所以你可以这样调用函数:
fadeOut("yourElementId", 1); //second parameter of your choice, accordingly.