var obj = {a: 1, b:2, c: 3};
function key_exists(k, o) {
    if (typeof o[k] != 'undefined') return true;
    else return false;
}
alert(key_exists('a', obj)); //true
alert(key_exists('d', obj)); //false

------解决方案--------------------
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http://www.cnblogs.com/snandy/archive/2011/03/04/1970162.html