looping through collection of javascript objects

Question

Am trying to read only very first element of friends array and add it to matches array for each object. If I add matches property directly on object. Then it returns expected result. But if I use a function addmatches to add matches array property. Then matches array value is coming same for each animal object.

var AnimalCreator = function(username, species, tagline, noises) {
  var friends = [];
   //var matches = [];
  return {
    username: username,
    species: species,
    tagline: tagline,
    noises: noises,
    friends: friends,
    //matches: matches
  }
};

var sheep = AnimalCreator('Cloud', 'sheep', 'You can count on me!', ['baahhh', 'arrgg', 'chewchewchew']);
var rabbit = AnimalCreator('Sky', 'Rabbit', 'I like jumping!', ['haha', 'heehee']);
var tiger = AnimalCreator('Tim', 'Tiger', 'I am strong!', ['Grrrr', 'grrrrrr!']);
var bear = AnimalCreator('Poo', 'Bear', 'I am your friend', ['wowo', 'whwhwh']);

var addFriend = function(animal, friend) {
  animal.friends.push(friend.username);
};

addFriend(sheep, rabbit);
addFriend(sheep, tiger);
addFriend(tiger, bear);

var myFarm = [sheep, rabbit, tiger, bear];

var addmatches  = function(farm){
  var matches = [];
  for(var i=0;i < farm.length; i++){
    farm[i].matches = matches;
  }
};

addmatches(myFarm);
var giveMatches = function(farm) {
  for (var i = 0; i < farm.length; i++) {
    if (farm[i].friends.length > 0) {
      farm[i].matches.push(farm[i].friends[0]);
    }
  }
};
giveMatches(myFarm);
console.log(myFarm);

Well, what is your addMatches function supposed to do? As of right now, assigning the same matches array to every animal is exactly what it does, and that's all it does. — JLRishe
– JLRishe, Commented Feb 12, 2019 at 17:23
addMatches function is adding 'matches' property to the object. — adi
– adi, Commented Feb 12, 2019 at 17:26
if I add matches propperty directly on object by uncommenting matches property in AnimalCreator function. And commenting out addmatches function. Notice matches array for each object . Why it's giving different values for matches property in these 2 scenarios — adi
– adi, Commented Feb 12, 2019 at 17:30

Prasun · Accepted Answer · 2019-02-12 17:25:07Z

2

matches is a reference to an empty array and your code is assigning same reference for every farm object ( farm[i].matches = matches; ), you can try by assigning empty array directly like

farm[i].matches = [];

Your commented code: The function AnimalCreator is creating a new array instance on every call and every animal object is referencing to a unique array, that's why when you directly add matches, it works as expected.

Hope this will help!

answered Feb 12, 2019 at 17:25

Prasun

5,0132 gold badges23 silver badges23 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Akash Jain · Accepted Answer · 2019-02-12 17:33:48Z

2

This is because array is passed by referance, so every farm object is pointing to the same array by this "farm[i].matches = matches;". To fix this you can do multiple tihings.

Change "farm[i].matches = matches;" to "farm[i].matches = [];" (Best option as of now).
Move "var matches = [];" inside for loop and use "let" insted of "var".

answered Feb 12, 2019 at 17:33

Akash Jain

292 bronze badges

Collectives™ on Stack Overflow

looping through collection of javascript objects

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related