向img滑块添加淡入淡出效果-纯JavaScript

所以，我知道jQuery使这变得非常简单，但我想知道如何在没有js库的情况下做到这一点。当此滑块中的图像更改时，如何合并淡入/淡出效果？我知道你可以用点符号来改变不透明度，我就是搞不懂它的逻辑

var myImg = document.querySelector('.imgSlot'),
  myImgArray = ["images/x.jpg", "images/y.jpg", "images/z.jpg", "images/abc.jpg"],
  imgIndex = 0,
  varTimerSpeed = 4000,
  intervalHandle = setInterval(changeImg, varTimerSpeed);

function changeImg() {
  myImg.setAttribute('src', myImgArray[imgIndex]);
  imgIndex++;
   if ( imgIndex >= myImgArray.length) {
        imgIndex = 0;
  }
};

任何建议都将不胜感激

---

David

您可以使用动画库来完成此操作。它使用setTimeout或setInterval函数每隔几毫秒应用对对象样式的更改，从而生成动画。 例如：

function moveElementToRight(el) {
    setInterval(function() {
       el.style.marginLeft = el.style.marginLeft + 10 //increase marginLeft by 10
    }),20) //every 20 milliseconds
}

一些基本逻辑：

var interval = 20 //milliseconds. Each 20 milliseconds = new frame.
var duration = 500 //milliseconds. Total time for the animation
var frames = Math.ceil(duration/interval) // frames count for the animation

您可以将该值与一个easing函数一起使用，该函数将通过将interval*i++从_值传递到_值duration来返回当前帧的值；这里我是通过循环帧计数获得的。From_值和to_值分别是元素的样式开始值和元素的样式结束值。这可能也适用于不透明度，这将导致褪色效果

这是一个非常粗略的例子，但这是主要原则。对于缓和效果，可以使用缓和功能。以下是一些：

    easeInQuad: function (t, b, c, d) {
        return c*(t/=d)*t + b;
    },
    easeOutQuad: function (t, b, c, d) {
        return -c *(t/=d)*(t-2) + b;
    },
    easeInOutQuad: function (t, b, c, d) {
        if ((t/=d/2) < 1) return c/2*t*t + b;
        return -c/2 * ((--t)*(t-2) - 1) + b;
    },
    easeOutCubic: function (t, b, c, d) {
        return c*((t=t/d-1)*t*t + 1) + b;
    },
    easeInOutCubic: function (t, b, c, d) {
        if ((t/=d/2) < 1) return c/2*t*t*t + b;
        return c/2*((t-=2)*t*t + 2) + b;
    },
    easeInQuart: function (t, b, c, d) {
        return c*(t/=d)*t*t*t + b;
    },
    easeOutQuart: function (t, b, c, d) {
        return -c * ((t=t/d-1)*t*t*t - 1) + b;
    },
    easeInOutQuart: function (t, b, c, d) {
        if ((t/=d/2) < 1) return c/2*t*t*t*t + b;
        return -c/2 * ((t-=2)*t*t*t - 2) + b;
    },
    easeInQuint: function (t, b, c, d) {
        return c*(t/=d)*t*t*t*t + b;
    },
    easeOutQuint: function (t, b, c, d) {
        return c*((t=t/d-1)*t*t*t*t + 1) + b;
    },
    easeInOutQuint: function (t, b, c, d) {
        if ((t/=d/2) < 1) return c/2*t*t*t*t*t + b;
        return c/2*((t-=2)*t*t*t*t + 2) + b;
    },
    easeInSine: function (t, b, c, d) {
        return -c * Math.cos(t/d * (Math.PI/2)) + c + b;
    },
    easeOutSine: function (t, b, c, d) {
        return c * Math.sin(t/d * (Math.PI/2)) + b;
    },
    easeInOutSine: function (t, b, c, d) {
        return -c/2 * (Math.cos(Math.PI*t/d) - 1) + b;
    },
    easeInExpo: function (t, b, c, d) {
        return (t==0) ? b : c * Math.pow(2, 10 * (t/d - 1)) + b;
    },
    easeOutExpo: function (t, b, c, d) {
        return (t==d) ? b+c : c * (-Math.pow(2, -10 * t/d) + 1) + b;
    },
    easeInOutExpo: function (t, b, c, d) {
        if (t==0) return b;
        if (t==d) return b+c;
        if ((t/=d/2) < 1) return c/2 * Math.pow(2, 10 * (t - 1)) + b;
        return c/2 * (-Math.pow(2, -10 * --t) + 2) + b;
    },
    easeInCirc: function (t, b, c, d) {
        return -c * (Math.sqrt(1 - (t/=d)*t) - 1) + b;
    },
    easeOutCirc: function (t, b, c, d) {
        return c * Math.sqrt(1 - (t=t/d-1)*t) + b;
    },
    easeInOutCirc:function (t, b, c, d) {
        if ((t/=d/2) < 1) return -c/2 * (Math.sqrt(1 - t*t) - 1) + b;
        return c/2 * (Math.sqrt(1 - (t-=2)*t) + 1) + b;
    },
    //a: amplitude (optional), p: period (optional)
    easeInElastic: function (t, b, c, d, a, p) {
        if (t===0) {return b;}
        if ((t/=d)==1) {return b+c;}
        if (!p) {p=d*0.3;}
        var s;
        if (a < Math.abs(c)) {
            a=c;
            s=p/4;
        }else {
            a=Math.abs(c);
            s = p/(2*Math.PI) * Math.asin(c/a);
        }
        return -(a*Math.pow(2,10*(t-=1)) * Math.sin( (t*d-s)*(2*Math.PI)/p )) + b;
    },
    easeOutElastic: function (t, b, c, d, a, p) {
        if (t===0) return b;
        if ((t/=d)==1) return b+c;
        if (!p) p=d*0.3;
        var s;
        if (a < Math.abs(c)) {
            a=c;
            s=p/4;
        }else {
            a=Math.abs(c);
            s = p/(2*Math.PI) * Math.asin (c/a);
        }
        return a*Math.pow(2,-10*t) * Math.sin( (t*d-s)*(2*Math.PI)/p ) + c + b;
    },
    easeInOutElastic: function (t, b, c, d, a, p) {
        if (t===0) return b;
        if ((t/=d/2)==2) return b+c;
        if (!p) p=d*(0.3*1.5);
        var s;
        if (a < Math.abs(c)) {
            a=c;
            s=p/4;
        }else {
            a=Math.abs(c);
            s = p/(2*Math.PI) * Math.asin (c/a);
        }
        if (t < 1) {
            return -0.5*(a*Math.pow(2,10*(t-=1)) * Math.sin( (t*d-s)*(2*Math.PI)/p )) + b;
        }
        return a*Math.pow(2,-10*(t-=1)) * Math.sin( (t*d-s)*(2*Math.PI)/p )*0.5 + c + b;
    },
    easeInBack: function (t, b, c, d, s) {
        if (s === undefined) s = 1.70158;
        return c*(t/=d)*t*((s+1)*t - s) + b;
    },
    easeOutBack: function (t, b, c, d, s) {
        if (s === undefined) s = 1.70158;
        return c*((t=t/d-1)*t*((s+1)*t + s) + 1) + b;
    },
    easeInOutBack: function (t, b, c, d, s) {
        if (s === undefined) s = 1.70158;
        if ((t/=d/2) < 1) return c/2*(t*t*(((s*=(1.525))+1)*t - s)) + b;
        return c/2*((t-=2)*t*(((s*=(1.525))+1)*t + s) + 2) + b;
    },
    easeInBounce: function (t, b, c, d) {
        return c - this.easeOutBounce (d-t, 0, c, d) + b;
    },
    easeOutBounce: function (t, b, c, d) {
        if ((t/=d) < (1/2.75)) {
            return c*(7.5625*t*t) + b;
        } else if (t < (2/2.75)) {
            return c*(7.5625*(t-=(1.5/2.75))*t + 0.75) + b;
        } else if (t < (2.5/2.75)) {
            return c*(7.5625*(t-=(2.25/2.75))*t + 0.9375) + b;
        } else {
            return c*(7.5625*(t-=(2.625/2.75))*t + 0.984375) + b;
        }
    },
    easeInOutBounce: function (t, b, c, d) {
        if (t < d/2) return this.easeInBounce (t*2, 0, c, d) * 0.5 + b;
        return this.easeOutBounce (t*2-d, 0, c, d) * 0.5 + c*0.5 + b;
    }

未经测试的示例：

function animate(element, property, start, end, interval, duration) {
    var frames = Math.ceil(duration/interval);
    for(i=0;i<=frames;i++) {
       (function(f){
           setTimeout(function() {
              element.style[property] = easing_function_from_above(interval*f, start, end,   duration);
           }, interval);
       })(i);
   }
}

---

我知道您要求使用纯JavaScript，但如果您尝试使用jQuery会更好，因为jQuery本身可以处理跨浏览器兼容性

您可以尝试以下方法：

$("#"+elem).fadeOut(1000, function () {
    var img = imgArr[currIndex];
    $("#"+elem).attr("src",img);
    $("#"+elem).fadeIn(1000);
});

它使用jqueryfadein和fadeOut机制来控制透明度。 检查下面的工作示例

---

这是个好问题。它确实帮助我学到了很多东西。不费吹灰之力，以下是我的想法：

注意：这仅用于淡入淡出，对其他样式的动画没有帮助

var fade = function (elementInDocument, fadeTo, amountOfTime) {
    var start = new Date().getTime(), //start with the beginning time
        getOpacity = function () {
            //returns the current opacity of the given element
            var cs = window.getComputedStyle(elementInDocument),
                co = cs.getPropertyValue('opacity');
            return parseFloat(co, 10); //getPropertyValue returns a string, 
                                       //so you need to float it
        },
        startingOpacity = getOpacity(), //the beginning opacity of the element
        diff = fadeTo - startingOpacity, //the difference between what you want the opacity to be 
                                         //and the beginning opacity
        timer = setInterval(function () {
            var co = getOpacity(), //start by getting the current opacity (each interval)
                runTime = new Date().getTime() - start, //the amount of time the function has run
                progress = runTime / amountOfTime; //the progress of the function

            if (progress >= 1) {
                clearInterval(timer); //stop the function because we have completed fade
            }
            //takes the beginning opacity and adds it to the product of the difference (diff) 
            //and progress of the function 
            elementInDocument.style.opacity = startingOpacity + (diff * progress); 
        }, 10);
};

//Then to call it
fade(document.getElementById("someElement"), .6, 3000);

我试图尽可能详细地解释

下面是一些测试用例：

另一个重要的注意事项是：这不是跨浏览器，尤其是在那些老的浏览器上