我的嵌套循环无法遍历对象数组

Question

I'm working on a free code camp question which is listed below:

FCC Question URL: https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/basic-javascript/profile-lookup

We have an array of objects representing different people in our contacts lists.

A lookUpProfile function that takes name and a property (prop) as arguments has been pre-written for you.

The function should check if name is an actual contact's firstName and the given property (prop) is a property of that contact.

If both are true, then return the "value" of that property. If name does not correspond to any contacts then return "No such contact". If prop does not correspond to any valid properties of a contact found to match name then return "No such property".

Here is the object:

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"]
    }
];

My Approach:

I am attempting to solve this problem by iterating through the arrays. So, we begin by iterating through the object (elements 0-3). If the firstName matches with name then we know it is in the Contacts[i] array. To find the property for the contacts[i] array, I will iterate through the array again to find Contacts[i].j === property.

Below is the code:

function lookUpProfile(name, prop){
// Only change code below this line

    for (var i = 0; i < contacts.length; i++){
         if (name === contacts[i].firstName){
             var val = contacts[i];
           for (var j = 0; j <val.length; j++){
                if (prop === val.j){
                    return val.j; 
                }else {
                  return  "No such property";
                }
            }
    }
    }
    return "No such contact"


// Only change code above this line
}

// Change these values to test your function
console.log(lookUpProfile("Bob", "number"));

For some reason, every time I run the function it says No such contact. I know that my outer loop works fine, but for some reason my inner loop doesn't?

I know that solutions include replacing my inner loop with the following statement:

if (contacts[x].hasOwnProperty(prop))

Or replacing the inner loop with this:

 if (prop in contacts[i]) {

However, I'm curious on why this method doesn't work? Any help would be much appreciated.

Here is the jsfiddle: https://jsfiddle.net/7u13cbm5/

Answer 1

// Only change code below this line

    for (var i = 0; i < contacts.length; i++){
         if (name === contacts[i].firstName){
             var val = contacts[i];
             for(var j in val) {
                if (val.hasOwnProperty(j) && prop === j){
                    return val[j]; 
                }
             }
             return "No such property";
         }
    }
    return "No such contact";


// Only change code above this line

Answer 2

Carefully consider what you're actually doing inside that inner loop.

What you're actually doing is using the dot notation to access the length and j property of the the contact that has a matching name.

In this cases particular case, you can try debugging by looking at what happens during each iteration of the loop by printing the values to console. For instance,

console.log(val.length) // ( => undefined) which means the loop wouldn't even run.

// Next let's look at val.j
for (var j = 0; j <val.length; j++){ 
  // If you added the following line to debug, 
  // you'll see that nothing would print because (j < val.length) is never true. 
  console.log(val.j) 
  if (prop === val.j){
    return val.j; 
  }else {
    return  "No such property";
  }
}

The reason why the console.log would not print is because you first try to access the length property of val, which does not exist for any contacts.

Try to pick up debugging in the future, even if it's just console.log and it would make your life a lot easier. Here's a great read if you have some time:https://medium.com/@mattburgess/beyond-console-log-2400fdf4a9d8 .