在数组的控制台对象中打印

Question

Hi I have been trying to learn Javascript using codeacademy.com and I have reached an exercise that doesn't seem to make any sense when why the exercise I have written.This is my code:

 (function(){
    var bob = {
        firstName: "Bob",
        lastName: "Jones",

        phoneNumber: "(650) 777 - 7777",
        email: "bob.jones@example.com"
    };

    var mary = {
        firstName: "Mary",
        lastName: "Johnson",

        phoneNumber: "(650) 888 - 8888",
        email: "mary.johnson@example.com"
    };

    var contacts = [bob, mary];

    var printPerson = function(person){
        console.log(person.firstName + " " + person.lastName);
    }

    var list = function(){
        var i = contacts.length;
        for(var j= 0; j < i ; j++){
            printPerson(contacts[i]);
        }
    };

        list();
})();

The problem is in the list function when I try to call the printPerson() function I get that person is undefined but if I write instead of the list() function this:

    printPerson(contacts[0]);
    printPerson(contacts[1]);

Everything works.What am I doing wrong in the list() function that it doesn't work?

Answer 1

var list = function(){
    var i = contacts.length;
    for(var j= 0; j < i ; j++){
        printPerson(contacts[i]);
    }
};

i here is a constant. If you replace it:

var list = function(){
    var i = contacts.length;
    for(var j= 0; j < contacts.length ; j++){
        printPerson(contacts[contacts.length]);
    }
};

For all arrays arr , arr[arr.length] will always be undefined. You probably want contacts[j] .

Answer 2

for(var j= 0; j < i ; j++){
    printPerson(contacts[i]); // this should be contacts[j]
}

Answer 3

contacts.forEach(function(contact) {
    printPerson(contact);
});

Answer 4

var bob = {
    firstName: "Bob",
    lastName: "Jones",
    phoneNumber: "(650) 777-7777",
    email: "bob.jones@example.com"
};

var mary = {
    firstName: "mary",
    lastName: "Johnson",
    phoneNumber: "(650) 888 - 8888",
    email: "mary.johnson@example.com"
};


 var contacts=[bob,mary];
 console.log(mary.phoneNumber);