how to use the unionby function from lodash in javascript

The unionBy function from lodash is used to merge multiple arrays and return a new array with unique values, based on a specific property. The syntax for using unionBy is:

index.tsx
_.unionBy([arrays], [iteratee=_.identity])
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Here, [arrays] is an array of arrays that needs to be merged, and [iteratee=_.identity] is an optional parameter which takes a function that is called for each element in the arrays to generate the value to be used for uniqueness comparison.

Let's say we have two arrays with objects having a productId property, and we want to merge them to get a new array with unique productId:

index.tsx
const _ = require('lodash');

const arr1 = [{productId: 1, product: "Apple"}, {productId: 2, product: "Banana"}];
const arr2 = [{productId: 3, product: "Orange"}, {productId: 2, product: "Banana"}];

const result = _.unionBy(arr1, arr2, 'productId');

console.log(result);
// Output: [{productId: 1, product: "Apple"}, {productId: 2, product: "Banana"}, {productId: 3, product: "Orange"}]
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Here, the third parameter 'productId' is used to identify unique elements during the merge. The resulting array will contain only one instance of each productId.

So, this is how you can use the unionBy function from lodash to merge arrays and return a new array with unique values based on a specific property.