for(var i in aArray) 和 for(i=0; i<aArray.length; i++)

function echo(s)
{
    document.write(s);
}

function in_array_orig(oItem, aArray)
{   
    for (var i=0; i<aArray.length; i++) if (aArray[i] == oItem) return true;

    return false;
}

function in_array_new(oItem, aArray)
{
    for (var i in aArray) if (aArray[i] == oItem) return true;

    return false;
}

var a = ["gab", "24", "manila"];

var aArr1 = [1];
var b = {0:aArr1, 1:24, 2:"manila"};

var aArr2 = [1];

echo(in_array_orig(24, a)); // true

echo(in_array_new(24, a));//true

echo(in_array_orig(24,b))//true
echo(in_array_new(24, b)); // true