Profile Lookup Exercise; Operator Question

JavaScript
1

Just curious about the operator on my for loop.
What’s the difference on setting up the condition as j <= contacts.length. to j < contacts.length?

I noticed that the code only works when I add the latter…

Your code so far


// Setup
var contacts = [
{
    "firstName": "Akira",
    "lastName": "Laine",
    "number": "0543236543",
    "likes": ["Pizza", "Coding", "Brownie Points"]
},
{
    "firstName": "Harry",
    "lastName": "Potter",
    "number": "0994372684",
    "likes": ["Hogwarts", "Magic", "Hagrid"]
},
{
    "firstName": "Sherlock",
    "lastName": "Holmes",
    "number": "0487345643",
    "likes": ["Intriguing Cases", "Violin"]
},
{
    "firstName": "Kristian",
    "lastName": "Vos",
    "number": "unknown",
    "likes": ["JavaScript", "Gaming", "Foxes"]
}
];


function lookUpProfile(name, prop){
// Only change code below this line
    for(var j = 0; j < contacts.length; j++){
        if(contacts[j].firstName == name){
            if(contacts[j].hasOwnProperty([prop])) return contacts[j][prop];
            else return 'No such property';
        }
    } return 'No such contact';

// Only change code above this line
}


// FOR DATA CHECKING
// console.log(contacts[3].firstName);
// console.log(contacts[3].hasOwnProperty('likes'));
// console.log(contacts[3].likes)

console.log(lookUpProfile('Kristian', 'lastName'));
console.log(lookUpProfile('Harry', 'likes'));

// lookUpProfile("Akira", "likes");

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/83.0.4103.61 Safari/537.36.

Challenge: Profile Lookup

Link to the challenge:

2

contacts[contacts.length] is undefined so when your code try to contacts[contacts.length].firstName it throws an error, and stops there, and your function doesn’t return anything

3

Can you explain a bit further? @_@

4

We start to count length of the array from 1, but index from 0, therefore array[array.length] can never exist:

length: | 1 | 2 | 3 | 4 | ... | n
--------------------------------------
index:  | 0 | 1 | 2 | 3 | ... | n - 1