Can't find the index of the matching object in a array of object

Question

I have a data

var data = {
  "variants": [{
      "quantity": "20",
      "varientId": 8,
      "currency": "YEN",
      "extraField": {
        "Size": "10",
        "Color": "Red",
        "Material": "Denim"
      },
      "price": "199"
    },
    {
      "quantity": "15",
      "varientId": 10,
      "currency": "YEN",
      "extraField": {
        "Size": "9",
        "Color": "Red",
        "Material": "Denim"
      },
      "price": "249"
    },
    {
      "quantity": "18",
      "varientId": 12,
      "currency": "YEN",
      "extraField": {
        "Size": "8",
        "Color": "Green",
        "Material": "Rubber",
      },
      "price": "279"
    }
  ]
}

and an object :

var obj = {
        "Size": "10",
        "Color": "Red",
        "Material": "Denim"
      }

I've tried this

var index = null

for(var l = 0; l<data.variants.length; l++){
  if(data.variants[l].extraField === obj){
     index = l  
  } 
}

console.log(index)

I've also tried using JSON.stringify:

JSON.stringify(data.variants[l].extraField) === JSON.stringify(obj)

I'm getting null when console logging the index variable but I should be getting 0 since the obj object matches the first variant's extrafield.

score 1 · Answer 1 · edited Jul 26 '23 at 15:46

The reason your current approach is not working is that you are trying to compare two objects directly using ===, which will not work for objects. In JavaScript, objects are compared by reference, not by their content, so even if two objects have the same key-value pairs, they will not be considered equal unless they are the same object in memory.

To find the index of the matching object in the array, you can use the JSON.stringify() method to compare the stringified versions of the objects. However, there is a more efficient and straightforward solution using a loop and comparing individual properties. Here's the easiest solution for your problem:

var data = {
  // Your data object here...
};

var obj = {
  // Your obj object here...
};

var index = null;

for (var l = 0; l < data.variants.length; l++) {
  var extraField = data.variants[l].extraField;
  var isEqual = true;

  for (var key in obj) {
    if (extraField.hasOwnProperty(key) && extraField[key] !== obj[key]) {
      isEqual = false;
      break;
    }
  }

  if (isEqual) {
    index = l;
    break;
  }
}

console.log(index);

This code will correctly find the index of the first object that matches the properties of the obj object within the data.variants array. It loops through each variant, compares the properties one by one, and breaks out of the loop as soon as it finds a matching variant, assigning the index to the index variable.

score 0 · Answer 2 · edited Jul 26 '23 at 15:48

The comparison of object with === really won't work, because they are different objects and you are comparing references to them. Alternatively, you can use a shallow comparison, checking each of the properties. But comparing via JSON.stringify is the right and simple solution in this case, and it works. By running this code, the number 0 will be displayed in the console, which is the index of the desired object.

var data = {
  "variants": [{
      "quantity": "20",
      "varientId": 8,
      "currency": "YEN",
      "extraField": {
        "Size": "10",
        "Color": "Red",
        "Material": "Denim"
      },
      "price": "199"
    },
    {
      "quantity": "15",
      "varientId": 10,
      "currency": "YEN",
      "extraField": {
        "Size": "9",
        "Color": "Red",
        "Material": "Denim"
      },
      "price": "249"
    },
    {
      "quantity": "18",
      "varientId": 12,
      "currency": "YEN",
      "extraField": {
        "Size": "8",
        "Color": "Green",
        "Material": "Rubber",
      },
      "price": "279"
    }
  ]
}

var obj = {
  "Size": "10",
  "Color": "Red",
  "Material": "Denim"
}

var index = null

for (var l = 0; l < data.variants.length; l++) {
  const isEqual = JSON.stringify(data.variants[l].extraField) === JSON.stringify(obj)
  if (isEqual) {
    index = l
  }
}

console.log(index)

Can't find the index of the matching object in a array of object

2 Answers2