How to Compare Two Object Arrays in JavaScript

Comparing arrays of objects in JavaScript requires more than a simple equality check. This article explores various techniques for effectively comparing two object arrays, providing detailed code examples and explanations to guide you through the process.

Understanding Object Array Declaration

Before diving into comparison methods, let’s review how to declare an array of objects in JavaScript:

let arrayOfObjects = [
  { propertyName: value, ... },
  { propertyName: value, ... },
  ...
];

Each object within the array is defined by curly braces {} and contains key-value pairs.

Comparison Techniques

Using every() and some()

This approach involves iterating through both arrays and comparing individual objects. We use the every() method to ensure that every object in the first array satisfies a condition. The condition is checked using the some() method, verifying if there’s at least one matching object in the second array. A match is determined by comparing specific property values.

function compareArrays(arr1, arr2) {
  return arr1.length === arr2.length && 
         arr1.every(obj1 => arr2.some(obj2 => 
           obj1.id === obj2.id && obj1.name === obj2.name
         ));
}


let arr1 = [{id:1, name:'apple'}, {id:2, name:'banana'}];
let arr2 = [{id:1, name:'apple'}, {id:2, name:'banana'}];

console.log(compareArrays(arr1, arr2)); //true


let arr3 = [{id:1, name:'apple'}, {id:2, name:'banana'}];
let arr4 = [{id:1, name:'apple'}, {id:2, name:'orange'}];

console.log(compareArrays(arr3, arr4)); //false

Leveraging Object.keys()

This method retrieves all the keys of an object. By iterating through the keys, we can compare corresponding property values between objects in the two arrays. This approach ensures that all properties of matching objects are equal.

function compareArrays(arr1, arr2) {
    return arr1.length === arr2.length &&
        arr1.every(obj1 => arr2.some(obj2 =>
            Object.keys(obj1).every(key => obj1[key] === obj2[key])
        ));
}

let arr1 = [{ id: 1, name: 'apple' }, { id: 2, name: 'banana' }];
let arr2 = [{ id: 1, name: 'apple' }, { id: 2, name: 'banana' }];
console.log(compareArrays(arr1, arr2));  // Output: true

let arr3 = [{ id: 1, name: 'apple' }, { id: 2, name: 'banana' }];
let arr4 = [{ name: 'apple', id: 1 }, { id: 2, name: 'banana' }];
console.log(compareArrays(arr3, arr4));  // Output: true  (order doesn't matter)


let arr5 = [{ id: 1, name: 'apple' }, { id: 2, name: 'banana' }];
let arr6 = [{ id: 1, name: 'apple' }, { id: 2, name: 'orange' }];
console.log(compareArrays(arr5, arr6));  // Output: false

Utilizing Lodash’s _.isEqual()

Lodash provides a powerful function, _.isEqual(), for deep comparison of objects and arrays. This function handles nested structures and complex comparisons efficiently.

const _ = require('lodash');

let arr1 = [{ id: 1, name: 'apple' }, { id: 2, name: 'banana' }];
let arr2 = [{ id: 1, name: 'apple' }, { id: 2, name: 'banana' }];

console.log(_.isEqual(arr1, arr2)); // true

Employing JSON.stringify()

This method converts objects into JSON strings, enabling comparison using string equality. However, this approach is sensitive to property order and may yield false negatives if the order differs between objects.

function compareArrays(arr1, arr2) {
    return JSON.stringify(arr1) === JSON.stringify(arr2);
}

let arr1 = [{ id: 1, name: 'apple' }, { id: 2, name: 'banana' }];
let arr2 = [{ id: 1, name: 'apple' }, { id: 2, name: 'banana' }];
console.log(compareArrays(arr1, arr2)); //Output : true

let arr3 = [{ id: 1, name: 'apple' }, { id: 2, name: 'banana' }];
let arr4 = [{ name: 'apple', id: 1 }, { id: 2, name: 'banana' }];
console.log(compareArrays(arr3, arr4)); //Output: false (order matters)

Conclusion

Comparing object arrays in JavaScript requires careful consideration of the comparison depth and property order. Choose the method that best suits your specific needs and data structure. Lodash’s _.isEqual() offers a robust solution for deep comparisons, while every() and some() provide more control over the comparison logic. JSON.stringify() offers a simple approach but should be used with caution due to its order sensitivity.