The _.unionBy() method accepts iteratee which is invoked for each element of each array to generate the criterion by which uniqueness is computed. The order of result values is determined from the first array in which the value occurs.
Syntax:
_.unionBy(array, [iteratee = _.identity])
Parameters: This method accepts two parameters as mentioned above and described below:
- array: This parameter holds the array to inspect.
- [iteratee = _.identity]: This parameter holds the iteratee invoked per element.
Return Value: This method is used to return the new array of combined values.
Example 1: Here, const _ = require(‘lodash’) is used to import the lodash library into the file.
Javascript
// Requiring the lodash library  const _ = require("lodash");    // Use of _.unionBy() method let gfg = _.unionBy([{ 'y': 1 }],                     [{ 'y': 2 }, { 'y': 1 }],                     [{ 'y': 3 }], 'y');         // Printing the output  console.log(gfg) |
Output:
[ { 'y': 1 }, { 'y': 2 }, {'y': 3} ]
Example 2:Â
Javascript
// Requiring the lodash library  const _ = require("lodash");    // Use of _.unionBy() method let gfg = _.unionBy([1.5],                     [2.6, 2.7],                     [2.3, 3.8], Math.floor);         // Printing the output  console.log(gfg) |
Output:
[1.5, 2.6, 3.8]
