为什么调用函数后它的对象属性值为undefined?

Question

var contacts = [

    {

        "firstName": "Akira",

        "lastName": "Laine",

        "number": "0543236543",

        "likes": ["Pizza", "Coding", "Brownie Points"]

    },

    {

        "firstName": "Harry",

        "lastName": "Potter",

        "number": "0994372684",

        "likes": ["Hogwarts", "Magic", "Hagrid"]

    }

    ];

function lookUp(p){

    alert(contacts[0].p);

}

lookUp("number");

上面的函数调用后，显示的结果是 undefined ,为什么不是 "0543236543" ？

Answer 1

alert(contacts[0][p]);