/**
 * 获取滚动的头部距离和左边距离
 * scroll().top scroll().left
 * @returns {*}
 */
function scroll() {
    if(window.pageYOffset !== null){
        return {
            top: window.pageYOffset,
            left: window.pageXOffset
        }
    }else if(document.compatMode === "CSS1Compat"){ // W3C
        return {
            top: document.documentElement.scrollTop,
            left: document.documentElement.scrollLeft
        }
    }

    return {
        top: document.body.scrollTop,
        left: document.body.scrollLeft
    }
}


function $(id) {
    return typeof id === "string" ? document.getElementById(id) : null;
}

/**
 * 获取屏幕的宽度和高度
 * @returns {*}
 */
function client() {
    if(window.innerWidth){ // ie9+ 最新的浏览器
        return {
            width: window.innerWidth,
            height: window.innerHeight
        }
    }else if(document.compatMode === "CSS1Compat"){ // W3C
        return {
            width: document.documentElement.clientWidth,
            height: document.documentElement.clientHeight
        }
    }

    return {
        width: document.body.clientWidth,
        height: document.body.clientHeight
    }
}


/**
 *  匀速动画函数
 * @param {object}obj
 * @param {number}target
 * @param {number}speed
 */
function constant(obj, target, speed) {
    // 1. 清除定时器
    clearInterval(obj.timer);

    // 2. 判断方向
    var dir = obj.offsetLeft < target ? speed : -speed;


    // 3. 设置定时器
    obj.timer = setInterval(function () {
        obj.style.left = obj.offsetLeft + dir + "px";

        if(Math.abs(target - obj.offsetLeft) < Math.abs(dir)){
            clearInterval(obj.timer);

            obj.style.left = target + "px";
            console.log(obj.offsetLeft, target);
        }
    }, 20);

}