looping thru array of objects

Question

hey guys so I'm trying to solve this problem here

Make a function that looks through a list (first argument) and returns an array of all objects that have equivalent property values (second argument).

but i can't seem to loop thru an array of objects if my life depended on it..... Here is my following code

function where(collection, source) {
  for(var prop in collection){
    if(collection.hasOwnProperty(prop)){
      console.log("collection." + prop + "=" + collection[prop]);
    }
  }
}

where([{ first: 'Romeo', last: 'Montague' }, { first: 'Mercutio', last: null }, { first: 'Tybalt', last: 'Capulet' }], { last: 'Capulet' });

i was reading documents on hasOwnProperty method and for in loops but it seems like I am utilizing them wrong, any guidance is appreciated, thanks.

THIS IS NOT A DUPLICATE

@WandMaker i havent gotten that far yet, I'm still struggling on how to iterate over an array of objects and print their keys and properties.....once i do that, thats a whole other ball park... — hello world
– hello world, Commented Jul 25, 2015 at 4:59
This question has been answered here - stackoverflow.com/questions/3010840/… — Wand Maker
– Wand Maker, Commented Jul 25, 2015 at 5:12

Community · Accepted Answer · 2017-05-23 10:26:37Z

1

The for...in loop is not what you want for iterating over arrays in javascript.

Use the sequential for loop to loop through the array, and the for..in loop to iterate over the keys of the object...

for(var i=0; i<collections.length; i+=1) {
  for(var prop in collections[i]){
    if(collections[i].hasOwnProperty(prop)){
      console.log("collection." + prop + "=" + collections[i][prop]);
    }
  }
}

edited May 23, 2017 at 10:26

CommunityBot

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answered Jul 25, 2015 at 4:55

sfletche

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2 Comments

hello world Over a year ago

so i just tested your code and i get the following console log collection.last=undefined ....

hello world Over a year ago

this looks good, I was told to use a for in loop, for this kind of stuff..... thanks for clarifying for me!

Wand Maker · Accepted Answer · 2015-07-25 11:28:17Z

1

One can use filter method to filter out elements that satisfy the condition. Also, since comparison of objects is needed in evaluating the condition, and there does not seem to be an equals method in JavaScript for Objects, one has to do additional work to check equality.

Here is one way the problem mentioned in question can be solved

function where(collection, source) {
  return collection.filter(function(item) { 
     return Object.keys(source).every(function(k){ return item[k] == source[k] });
  });
}

console.log (where([{ first: 'Romeo', last: 'Montague' }, { first: 'Mercutio', last: null }, { first: 'Tybalt', last: 'Capulet' }], { last: 'Capulet'}));

Output

[ { first: 'Tybalt', last: 'Capulet' } ]

answered Jul 25, 2015 at 11:28

Wand Maker

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