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/**
 * Define the chunk method in the prototype of an array
 * that returns an array with arrays of the given size (with a recursive function).
 *
 * @param chunk_size {Integer} Size of every group
 */
Array.prototype.chunk = function (chunk_size) {
    if ( !this.length ) {
        return [];
    }

    return [ this.slice( 0, chunk_size ) ].concat(this.slice(chunk_size).chunk(chunk_size));
};

/**
 * Returns an array with arrays of the given size.
 *
 * @param myArray {Array} Array to split
 * @param chunkSize {Integer} Size of every group
 */
function chunkArray(myArray, chunk_size){
    var results = [];
    
    while (myArray.length) {
        results.push(myArray.splice(0, chunk_size));
    }
    
    return results;
}

// Split in group of 3 items
var result = chunkArray([1,2,3,4,5,6,7,8], 3);
// Outputs : [ [1,2,3] , [4,5,6] ,[7,8] ]
console.log(result);

/**
 * Define the chunk method in the prototype of an array
 * that returns an array with arrays of the given size.
 *
 * @param chunkSize {Integer} Size of every group
 */
Object.defineProperty(Array.prototype, 'chunk', {
    value: function(chunkSize) {
        var that = this;
        return Array(Math.ceil(that.length/chunkSize)).fill().map(function(_,i){
            return that.slice(i*chunkSize,i*chunkSize+chunkSize);
        });
    }
});

// Split in group of 3 items
var result = [1,2,3,4,5,6,7,8].chunk(3);
// Outputs : [ [1,2,3] , [4,5,6] ,[7,8] ]
console.log(result);

/**
 * Define the chunk method in the prototype of an array
 * that returns an array with arrays of the given size.
 *
 * @param chunkSize {Integer} Size of every group
 */
Object.defineProperty(Array.prototype, 'chunk', {
    value: function(chunkSize){
        var temporal = [];
        
        for (var i = 0; i < this.length; i+= chunkSize){
            temporal.push(this.slice(i,i+chunkSize));
        }
                
        return temporal;
    }
});
// Split in group of 3 items
var result = [1,2,3,4,5,6,7,8].chunk(3);
// Outputs : [ [1,2,3] , [4,5,6] ,[7,8] ]
console.log(result);

/**
 * Returns an array with arrays of the given size.
 *
 * @param myArray {Array} array to split
 * @param chunk_size {Integer} Size of every group
 */
function chunkArray(myArray, chunk_size){
    var index = 0;
    var arrayLength = myArray.length;
    var tempArray = [];
    
    for (index = 0; index < arrayLength; index += chunk_size) {
        myChunk = myArray.slice(index, index+chunk_size);
        // Do something if you want with the group
        tempArray.push(myChunk);
    }

    return tempArray;
}
// Split in group of 3 items
var result = chunkArray([1,2,3,4,5,6,7,8], 3);
// Outputs : [ [1,2,3] , [4,5,6] ,[7,8] ]
console.log(result);