Javascript解决方案：

function resizableStart(e){
    this.originalW = this.clientWidth;
    this.originalH = this.clientHeight;
    this.onmousemove = resizableCheck;
    this.onmouseup = this.onmouseout = resizableEnd;
}
function resizableCheck(e){
    if(this.clientWidth !== this.originalW || this.clientHeight !== this.originalH) {
        this.originalX = e.clientX;
        this.originalY = e.clientY;
        this.onmousemove = resizableMove;
    }
}
function resizableMove(e){
    var newW = this.originalW + e.clientX - this.originalX,
        newH = this.originalH + e.clientY - this.originalY;
    if(newW < this.originalW){
        this.style.width = newW + 'px';
    }
    if(newH < this.originalH){
        this.style.height = newH + 'px';
    }
}
function resizableEnd(){
    this.onmousemove = this.onmouseout = this.onmouseup = null;
}

var els = document.getElementsByClassName('resizable');
for(var i=0, len=els.length; i<len; ++i){
    els[i].onmouseover = resizableStart;
}

上面的解决方案使用mouseover和mouseout触发resizableStart和resizableEnd。问题是，如果要调整大小的元素具有子元素，则将鼠标放在子元素上时，该元素会收到一个mouseout事件，并且紧随其后，它会收到一个mouserover从子元素冒泡的事件。