Group Array Elements

Write a JavaScript program to group array elements based on a specific criterion. The function should take an array of objects and a key, then group the objects by the values of that key. Return an object where each key represents a unique value from the specified property, and the value is an array of objects that have that property value.

Example 1

  
Input: arr = [{name: "Alice", age: 25}, {name: "Bob", age: 25}, {name: "Charlie", age: 30}], key = "age"
  
Output: {25: [{name: "Alice", age: 25}, {name: "Bob", age: 25}], 30: [{name: "Charlie", age: 30}]}
  
Explanation: 
Initialize an empty result object to store grouped elements. 
Process first object {name: "Alice", age: 25} - create group for age 25. 
Process second object {name: "Bob", age: 25} - add to existing age 25 group. 
Process third object {name: "Charlie", age: 30} - create new group for age 30. 
Return the grouped object with two groups: age 25 and age 30.

Example 2

  
Input: arr = [{type: "fruit", name: "apple"}, {type: "vegetable", name: "carrot"}, {type: "fruit", name: "banana"}], key = "type"
  
Output: {fruit: [{type: "fruit", name: "apple"}, {type: "fruit", name: "banana"}], vegetable: [{type: "vegetable", name: "carrot"}]}
  
Explanation: 
Start with an empty result object. Group apple under "fruit" category. 
Group carrot under "vegetable" category. 
Add banana to existing "fruit" group. 
Return object with two groups: fruit and vegetable.

Constraints

  
1 ≤ arr.length ≤ 1000
  
Each object in the array contains the specified key
  
The key value can be string, number, or boolean
  
Time Complexity: O(n) where n is the length of the array
  
Space Complexity: O(n) for storing the grouped result