How can I retrieve the object into an array in Javascript?

Question

I'm currently practicing some basic problem in js and fairly new to any of these languages. I want to retrieve the value and name of the property into an array "temp" from the object "second" if the another obj "third" has the same property value. I can do it, when the property name is already defined, but how can I do the same if I don't know the actual property name. May be using Object.keys()

My code is something like this:

      function where(second, third) {
  var arr = [];
  var temp=[];
  for(var i in second)
    {

      if(third.hasOwnProperty('last')){
        if(second[i].last===third.last){
          arr=second[i];
          temp.push(arr);
        }
      }
      if(third.hasOwnProperty('first')){
        if(second[i].first===third.first){
          arr=second[i];
          temp.push(arr);
        }
      }

    }
  return temp;
}

where([{ first: 'Ram', last: 'Ktm' }, { first: 'Sam', last: null }, { first: 'Tybalt', last: 'Capulet' }], { last: 'Capulet' });

The resulting array is : [{ 'first': 'Tybalt', 'last': 'Capulet' }]

How can I retrieve the same result even if I don't know the actual property name. For instance the name here first and last might be food, and uses which is unknown. I've already gone with the following threads here.

[2]: https://stackoverflow.com/questions/4607991/javascript-transform-object-into-array

[1]: https://stackoverflow.com/questions/4607991/javascript-transform-object-into-array

@fuyushimoya, just corrected that it meant to be for(var i in second). — user2906838
– user2906838, Commented Jun 20, 2015 at 8:29

Nina Scholz · Accepted Answer · 2015-06-20 10:12:09Z

1

function where(second, third) {
    var temp = [];
    var k = Object.keys(third)[0]; // expecting only one element!
    second.forEach(function (obj) {
        if (obj[k] === third[k]) {
            temp.push(obj);
        }
    });
    return temp;
}

edited Jun 20, 2015 at 10:12

answered Jun 20, 2015 at 8:38

Nina Scholz

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1 Comment

Nina Scholz Over a year ago

obj is a parameter of the callback function.

Knight Yoshi · Accepted Answer · 2015-06-20 09:02:24Z

1

I think the getOwnPropertyName is what you're looking for. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/getOwnPropertyNames

Object.getOwnPropertyNames({a:1,2:"b",c:"a"}).sort() // returns Array [ "2", "a", "c" ]

I'll expand on my initial answer

var temp = [];

var myobj = [{cat:"Felix",dog:"Milo",bird:"Monkey",3:"pets"}, 
         {cat:"Wiskers",dog:"yapper",bird:"tweeter",1:"human"}];

var myobj2 = {cat:"Harry",dog:"Fuzz",1:"human"};

var objKeys = Object.getOwnPropertyNames(myobj); //will have key "1" that matches below

objKeys.forEach(function(key) {
    if(myobj2.hasOwnProperty(key)) {
        temp.push(myobj2[key]) // will push "human" to temp array
    }
})

edited Jun 20, 2015 at 9:02

answered Jun 20, 2015 at 8:31

Knight Yoshi

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4 Comments

user2906838 Over a year ago

that's looks pretty and short but I'm not sure, will try to use this.

Knight Yoshi Over a year ago

whoops. I actually forgot something. Helping people at 5am may not be a good thing.. Need to loop myobj to get each object's keys :<

Knight Yoshi Over a year ago

I think Nina Scholz's answer is probably the best.

user2906838 Over a year ago

Thanks! I must appreciate your support and I do.

fuyushimoya · Accepted Answer · 2015-06-20 08:37:07Z

0

function where(second, third) {
  var tmp = [];
  var length = second.length;

  var i, k, test;
  // Go through second's each item to see that...
  for (i = 0; i < length; ++i) {
    test = second[i];
    // For all key in third that belongs to third (not inherited or else)
    for (k in third) {
      // Check has own property.
      if (!third.hasOwnProperty(k)) {
        continue;
      }
      // If second[i] don't have key `k` in second or second[i][k]'s value is 
      // not equal to third[k], then don't put it into tmp, start to check next.
      if (!third.hasOwnProperty(k)) {
        break;
      } else if (test[k] !== third[k]) {
        break;
      }
      tmp.push(test);
    }
  }
  return tmp;
}

edited Jun 20, 2015 at 8:37

answered Jun 20, 2015 at 8:29

fuyushimoya

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8 Comments

user2906838 Over a year ago

@fuyshimoya , thank you! I couldn't even vote up. You perfectly filtered the value of the "third".

fuyushimoya Over a year ago

I edited, for you use the hasOwnProperty, which you may concern if your object is extended or created by some extended prototypes.

user2906838 Over a year ago

What would be the approach, If I wish to use Object.keys(). Assume I'm very newbie.

user2906838 Over a year ago

@fuyushimoya, ya hasOwnProperty seems not a good idea, actually I didn't know how else I could go. So I just thought using it should be in very lower level to understand, actually your first answer was more understandable but this too is fairly simple. Thank you for clarifying me.

fuyushimoya Over a year ago

I'm not sure why you think hasOwnProperty is not a good idea, it's good or not depends on how you create the object you want to test, anyway, if you accept Nina Scholz' s answer, notify her that her answer will only check first key of the object, so if there's more than 1 key in third, outcome might not be what you want.

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