oa1.onmousemove = function (ev) {
            var oEvnt = ev || event;
            var x     = oEvnt.clientX - oa1.offsetLeft;
            var y     = oEvnt.clientY - oa1.offsetTop;
            console.log(x, y);
            oa2.style.left = -(x * 2 - 100) + 'px';//问题用clientWidth为什么是NAN
            oa2.style.top = -(y * 2 - 100) + 'px';
            if (x >= oa1.clientWidth - (op.clientWidth / 2)) {
                op.style.top = oa1.clientHeight - op.clientHeight + "px";

            } else {
                op.style.top = y - 50 + "px";

            }
            if (oEvnt.clientY - oa1.offsetTop >= oa1.clientHeight - op.clientHeight / 2) {
                op.style.left = oa1.clientWidth - op.clientWidth + "px"
            } else {

                op.style.left = x - 50 + "px";
            }
        };
        
    

在上面的if条件我想的是当鼠标划到离a标签边距只有50px就让p的top值固定为一个值。

上面只是部分代码。也许我用判断语句不是很合适，请教这位大神如何解决？