<style type="text/css">
    .slider {
        position: relative;
        overflow: hidden;
        min-height: 1px;
    }

    .slider-groups {
        position: relative;
        overflow: hidden;
        white-space: nowrap;
    }

    .slider-item {
        float: left;
        box-sizing: border-box;
        overflow: hidden;
        /*text-align: center;*/
        animation: switch 5s ease-out infinite;
    }

    .slider-item a {
        display: block;
        width: 100%;
        overflow: hidden;
        text-decoration: none;
    }

    .slider-item img {
        display: block;
        width: 100%;
    }

    /*    right: 0;left: 0; 是为了使width为100%，
有了宽度text-align才能生效，当然你直接写width:100%也行*/

    @keyframes switch {

        0%,
        45% {

            margin-left: 0;

        }

        55%,
        100% {

            margin-left: -12.5%;

        }

    }
    </style>

<div class="slider">
            <div class="slider-group">
                <div class="slider-item">
                    <a href="javascript:;">
                        <img src="__PUBLIC__/assets/images/index/banner_1.jpg">
                    </a>
                </div>
                <div class="slider-item">
                    <a href="javascript:;">
                        <img src="__PUBLIC__/assets/images/index/banner_2.jpg">
                    </a>
                </div>
            </div>
        </div>

window.onload = function() {
        setSliderWidth();
    }

function setSliderWidth() {
    const p = document.getElementsByClassName('slider')[0];
    const c = document.getElementsByClassName('slider-group')[0];
    const ifLoop = true;

    let children = c.children;
    let width = 0;
　　//注意三个xxWidth值的区别，clientWidth包含了页面右侧滑轨的宽度
    // let sliderWidth = p.clientWidth;
    // let sliderWidth = p.offsetWidth;
    let sliderWidth = window.innerWidth;
    for(let i=0;i<children.length;i++) {
        let child = children[i];
        child.style.width = sliderWidth + 'px';
        width += sliderWidth;
    };
    if(ifLoop) {
        width += 2 * sliderWidth;
    };
    c.style.width = width + 'px';
}