GroupBy.js

// As a prototype

/* 
 * @param property string - The object propperty to group by.
 */
Array.prototype.groupBy = function (property) {
  const filtered = this.reduce(function(item, x) {
    if (!item[x[property]]) { item[x[property]] = []; }
    item[x[property]].push(x);
    return item;
  }, []);

    const temp = {};
    Object.keys(filtered).forEach(i => temp[i] = filtered[i]);

	return temp;
}

// As a function

/* 
*  @param arr array - The array to group.
 * @param property string - The object propperty to group by.
 */

export const groupBy = function (arr, property) {
  const filtered = arr.reduce(function(item, x) {
    if (!item[x[property]]) { item[x[property]] = []; }
    item[x[property]].push(x);
    return item;
  }, []);

    const temp = {};
    Object.keys(filtered).forEach(i => temp[i] = filtered[i]);

	return temp;
}