how to test whether a object has member
Object.prototype.hasMember = function (memberName) { return memberName in this; } var attrFn = { val: 1, css: 2, html: 3, text: 4, data: 5, width: 6, height: 7, offset: 8 }; alert(attrFn.hasMember("val")); /* don't use attrFn["val"], because is possible that you defined a member attFn = { val : undefined }, in val is a member but its value is null, this function also traverse the prototype chain, if you want to check direct member only use "hasOwnProperty". */