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how to make a function that looks thru first argument and returns an array that is equal to the second argument

I'm making a function that looks thru an array of the first argument and returns an array with all the objects that are matching the second argument. i dont know what is wrong with my code or how to fix it. i would appreciated it if you can help me

function whatIsInAName(collection, source) {
  const arr = [];
  // Only change code below this line
  for (let i=0; i<collection.length; i++) {
    if (source.hasOwnProperty(collection[i])) {
      arr.push(collection[i])
    }

  }

  // Only change code above this line
  return arr;
}

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

about 4 years ago · Juan Pablo Isaza

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Answer 1 · 2022-07-10T08:27:32.918Z

I'm assuming you only want to match the last field in a object.

function whatIsInAName(collection, source) {
  return collection.filter(({ last }) => last === source.last);
}

const result = whatIsInAName(
  [
    { first: "Romeo", last: "Montague" },
    { first: "Mercutio", last: null },
    { first: "Tybalt", last: "Capulet" },
  ],
  { last: "Capulet" }
);

console.log(result);

Here we're just using a Filter Method on the collection array. The function predicate (({ last }) => last === source.last) we're passing in the filter will receive each object from the collection and check if source.last === received.last.

The is the same as the following one:

function doesMatch(receivedObject) {
    if(receivedObject.last === source.last) return true;
    else return false;
}

Answer 2 · 2022-07-10T08:27:32.925Z

This is why source.hasOwnProperty isn't working as expected:

If you run console.log you will see that you are looping through the elements in collection which are objects.

Example:

function whatIsInAName(collection, source) {
  const arr = [];
  // Only change code below this line
  for (let i=0; i<collection.length; i++) {
    console.log(collection[i]);
    if (source.hasOwnProperty(collection[i])) {
      arr.push(collection[i])
    }

  }

  // Only change code above this line
  return arr;
}

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

But what you actually want to do (if you're checking properties, aka keys) is loop through the keys in each object.

For that, you need a second loop inside the first.

the first loop will cycle through the object elements
the second loop will cycle through the keys in each object element

Usefully, you can use:

Object.keys()

to return an array of object keys (for each object) to loop through.

So your second loop can be another for loop.

Example:

function whatIsInAName(collection, source) {
  const arr = [];
  
  // Only change code below this line
  for (let i=0; i<collection.length; i++) {
  
    // Object Keys to Loop Through
    let myKeys = Object.keys(collection[i]);

    // Object Values
    let myValues = Object.values(collection[i]);
    
    for (let j = 0; j < myKeys.length; j++) {
      
      if ((source.hasOwnProperty(myKeys[j])) && (source[myKeys[j]] === myValues[j])) {
        arr.push(collection[i])
      }
    }
  }
  
  console.log(arr);

  // Only change code above this line
  return arr;
}

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

Answer 3 · 2022-07-10T08:27:32.931Z

This is the mistake:

if (source.hasOwnProperty(collection[i])) {
//                        ^ collection[i] is an object, not a property

It may be an idea to use Array.filter here. Something like:

const whatIsInAName = (collection, source) => {
  // compare for all keys keys in [source]
  const compare = (obj1, obj2, keys) => 
    keys.filter( k => obj1[k] === obj2[k] ).length > 0;
  // filter using comparison method
  return collection.filter( r => compare(source, r, Object.keys(source)) );
};
const collection2CompareTo = [
  { first: "Romeo", last: "Montague" }, 
  { first: "Mercutio", last: null }, 
  { first: "Tybalt", last: "Capulet" }];
// expect: [{ first: "Tybalt", last: "Capulet" }], 
const c1 = whatIsInAName(collection2CompareTo, { last: "Capulet" });
// expect: [{ first: "Romeo", last: "Montague" }]
const c2 = whatIsInAName(collection2CompareTo, { first: "Romeo" });
// expect: [{ first: "Romeo", last: "Montague" }]
const c3 = whatIsInAName(collection2CompareTo, { first: "Romeo", last: "Montague" });
// expect: []
const c4 = whatIsInAName(collection2CompareTo, { first: undefined, last: "Void" });

document.querySelector(`pre`).textContent = `c1: ${
  JSON.stringify(c1, null, 2)}\nc2: ${
  JSON.stringify(c2, null, 2)}\nc3: ${
  JSON.stringify(c3, null, 2)}\nc4: ${
  JSON.stringify(c4, null, 2)}`;

<pre></pre>

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how to make a function that looks thru first argument and returns an array that is equal to the second argument

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