滚动条监听

function procScroll(selector, xPercent, xCallback, yPercent, yCallback) {
    var _isType = function(obj, type) {
        return Object.prototype.toString.call(obj) === '[object ' + type + ']';
    };

    var isString = _isType(selector, 'String');
    if (!isString || (isString && (selector.length < 2))) {
        return null;
    }

    if ((xPercent <= 0) || (xPercent > 1) && ((yPercent <= 0) || (yPercent > 1))) {
        return null;
    }

    if (!_isType(xCallback, 'Function') && !_isType(yCallback, 'Function')) {
        return null;
    }

    var lstObj = document.querySelectorAll(selector);
    if (lstObj.length < 1) {
        return null;
    }

    var obj = lstObj[0];
    var isProc = {
        'x': false,
        'y': false,
    };

    obj.onscroll = function(e) {
        if (isProc.x === false) {
            if ((0 < xPercent) && (xPercent <= 1)) {
                if (((obj.scrollLeft + obj.clientWidth) / obj.scrollWidth) >= xPercent) {
                    isProc.x = true;
                    _isType(xCallback, 'Function') && xCallback(function() {
                        isProc.x = false;
                    });
                }
            }
        }

        if (isProc.y === false) {
            if ((0 < yPercent) && (yPercent <= 1)) {
                if (((obj.scrollTop + obj.clientHeight) / obj.scrollHeight) >= yPercent) {
                    isProc.y = true;
                    _isType(yCallback, 'Function') && yCallback(function() {
                        isProc.y = false;
                    });
                }
            }
        }
    };
}

procScroll('.img-wrap', .7, function(_done) {
    setTimeout(function() {
        _done();
        alert('x');
    }, 2000);
}, .8, function(_done) {
    setTimeout(function() {
        _done();
        alert('y');
    }, 2000);
});