使用js实现div的缩放代码

现在遇到一个问题，实现div在某个div范围内的缩放，目前是已经做好了缩放的功能，但是不太会做边界判断，希望各路大神能够给予帮助！！！
一下是实现了缩放的代码：
`/**
*
* @param {object} obj1 要缩放的元素
* @param {object} obj2 控制的节点
*/
function dragFn(obj1, obj2) {

        obj2.onmousedown = function(ev) {

            reszing = true;

            draping = false;

            var oEv = ev || event;

            oEv.stopPropagation();

            var oldWidth = obj1.offsetWidth;

            var oldHeight = obj1.offsetHeight;

            var oldX = oEv.clientX;

            var oldY = oEv.clientY;

            var oldLeft = obj1.offsetLeft;

            var oldTop = obj1.offsetTop;

            document.onmousemove = function(ev) {
                var oEv = ev || event;

                if(obj2.className == 'resizeLT') {

                    obj1.style.width = oldWidth - (oEv.clientX - oldX) + 'px';

                    obj1.style.height = oldHeight - (oEv.clientY - oldY) + 'px';

                    obj1.style.left = oldLeft + (oEv.clientX - oldX) + 'px';

                    obj1.style.top = oldTop + (oEv.clientY - oldY) + 'px';

                    //                      console.log(obj1.style.left, obj1.style.top);

                } else if(obj2.className == 'resizeLB') {

                            // if(oldLeft + (oEv.clientX - oldX)<0){
                            //  reszing = false;
                            // }
                            // if(oldTop + (oEv.clientY + oldY)<0){
                            //  reszing = false;
                            // }    
                    obj1.style.width = oldWidth - (oEv.clientX - oldX) + 'px';

                    obj1.style.height = oldHeight + (oEv.clientY - oldY) + 'px';

                    obj1.style.left = oldLeft + (oEv.clientX - oldX) + 'px';

                    obj1.style.bottom = oldTop + (oEv.clientY + oldY) + 'px';

                } else if(obj2.className == 'resizeTR') {

                    //          if(oldLeft - (oEv.clientX - oldX)<0){
                    //              document.onmousemove=null;
                    //          }
                    //          if(oldTop + (oEv.clientY - oldY)<0){
                    //              document.onmousemove=null;
                    //          }   

                    obj1.style.width = oldWidth + (oEv.clientX - oldX) + 'px';

                    obj1.style.height = oldHeight - (oEv.clientY - oldY) + 'px';

                    obj1.style.right = oldLeft - (oEv.clientX - oldX) + 'px';

                    obj1.style.top = oldTop + (oEv.clientY - oldY) + 'px';

                } else if(obj2.className == 'resizeBR') {

                    //          if(oldLeft - (oEv.clientX - oldX)<0){
                    //              
                    //              document.onmousemove=null;
                    //          }
                    //          if(oldTop + (oEv.clientY + oldY)<0){
                    //              
                    //              document.onmousemove=null;
                    //          }   
                    //          
                    obj1.style.width = oldWidth + (oEv.clientX - oldX) + 'px';

                    obj1.style.height = oldHeight + (oEv.clientY - oldY) + 'px';

                    obj1.style.right = oldLeft - (oEv.clientX - oldX) + 'px';

                    obj1.style.bottom = oldTop + (oEv.clientY + oldY) + 'px';

                } else if(obj2.className == 'resizeT') {

                    //          if(oldTop + (oEv.clientY - oldY)<0){
                    //              
                    //              document.onmousemove=null;
                    //          }

                    obj1.style.height = oldHeight - (oEv.clientY - oldY) + 'px';

                    obj1.style.top = oldTop + (oEv.clientY - oldY) + 'px';

                } else if(obj2.className == 'resizeB') {

                    //          if(oldTop - (oEv.clientY + oldY)<0){
                    //              
                    //              document.onmousemove=null;
                    //          }

                    obj1.style.height = oldHeight + (oEv.clientY - oldY) + 'px';

                    obj1.style.bottom = oldTop - (oEv.clientY + oldY) + 'px';

                } else if(obj2.className == 'resizeL') {

                    //          if(oldLeft + (oEv.clientX - oldX)<0){
                    //              
                    //              document.onmousemove=null;
                    //          }       

                    obj1.style.height = oldHeight + 'px';

                    obj1.style.width = oldWidth - (oEv.clientX - oldX) + 'px';

                    obj1.style.left = oldLeft + (oEv.clientX - oldX) + 'px';

                } else if(obj2.className == 'resizeR') {

                    //          if( oldLeft - (oEv.clientX - oldX)<0){
                    //              
                    //              document.onmousemove=null;
                    //          }

                    obj1.style.height = oldHeight + 'px';

                    obj1.style.width = oldWidth + (oEv.clientX - oldX) + 'px';

                    obj1.style.right = oldLeft - (oEv.clientX - oldX) + 'px';
                }
                console.log("resizeW:"+obj1.style.left,"resizeH:"+obj1.style.top);
                
            };

            document.onmouseup = function() {
                document.onmousemove = null;
            };
            return false;
        };
    }`