Question

i write a function want to set or get style property value:

function $(ID){return document.getElementById(ID);}

Object.prototype.css=function(style,value){
    if(value==undefined){
        return eval("this.style."+style);
    }
    else{
        if(isNaN(value)){
            return eval("this.style."+style+"=\""+value+"\"");
        }
        else{
            return eval("this.style."+style+"="+value);
        }
    }
}

function ad(){
    $("ad_ol").css("top","-170px");
}

it can work well in FireFox 、 Chrome and IE9,but not work in IE7 and IE8,error message is:Object does not support the “css” property or method

who can help me? is the “this” problem? is have better function can do this?

Answer 1

No need for eval, and there are other flaws in you code.
Try using something like:

function css(prop,value){
  value = value || '';

  if(prop) {
    this.style[prop] = value;
    return this.style[prop];
  }
  return true;
}

function $(ID){
  var element = document.getElementById(ID || 'nodId');

  if(element) {
    element.css = css; // create css method for this element
  }

  return element; // Note: element is null if no ID was provided
}

$("ad_ol").css("top","-170px"); //=> should work now