新浪微博 鼠标悬停到用户头像时弹出的card是怎么实现的

Tooltip.prototype.show = function() {

    elTopLocation = this.getBoundingClientRect().top;
    elBottomLocation = window.innerHeight - this.getBoundingClientRect().bottom;
    elLeftLocation = this.getBoundingClientRect().left;
    elRightLocation = window.innerWidth - this.getBoundingClientRect().right;

    var direction;
    direction = elLeftLocation < minVerticalDistance ? 'right' : 'left';
    direction = elBottomLocation < minHorizonDistance ? 'top' : 'bottom';

    $(this).addClass('hint hint--'+direction);
    return this.direction = direction;
};