Lots of Chunking Options

chunk.js

// --- Directions
// Given an array and chunk size, divide the array into many subarrays
// where each subarray is of length size
// --- Examples
// chunk([1, 2, 3, 4], 2) --> [[ 1, 2], [3, 4]]
// chunk([1, 2, 3, 4, 5], 2) --> [[ 1, 2], [3, 4], [5]]
// chunk([1, 2, 3, 4, 5, 6, 7, 8], 3) --> [[ 1, 2, 3], [4, 5, 6], [7, 8]]
// chunk([1, 2, 3, 4, 5], 4) --> [[ 1, 2, 3, 4], [5]]
// chunk([1, 2, 3, 4, 5], 10) --> [[ 1, 2, 3, 4, 5]]

function chunk(array, size) {
  const arr = [];
  let i = 0;
  while (i < array.length) {
    arr.push(array.slice(i, i + size));
    i = i + size;
  }
  return arr;
}

module.exports = chunk;

// Native JS via slice
function forSlice(array, size) {
  const arr = [];
  for (let i = 0; i < array.length; i += size) {
    arr.push(array.slice(i, i + size));
  }
  return arr;
}

// Native JS via slice while
function whileSlice(array, size) {
  const arr = [];
  let i = 0;
  while (i < array.length) {
    arr.push(array.slice(i, i + size));
    i = i + size;
  }
  return arr;
}

// Multiple loops
function multiLoop(array, size) {
  const arr = [];
  for (let i = 0; i < array.length; i += size) {
    const subArr = [];
    for (let k = 0; k < size && i + k < array.length; k++) {
      subArr.push(array[i + k]);
    }
    arr.push(subArr);
  }
  return arr;
}

// Single loop with last item reference
function holdReference(array, size) {
  const arr = [];
  let window = [];
  for (let i = 0; i < array.length; i++) {
    if (i !== 0 && i % size === 0) {
      arr.push(window);
      window = [];
    }
    window.push(array[i]);
  }
  if (window.length > 0) {
    arr.push(window);
  }
  return arr;
}

// Single loop with last item fetch
function forLastItem(array, size) {
  const arr = [[]];
  for (let i = 0; i < array.length; i++) {
    let lastChunk = arr[arr.length - 1];
    if (lastChunk.length < size) {
      lastChunk.push(array[i]);
    } else {
      arr.push([array[i]]);
    }
  }
  return arr;
}

// Single loop with last item fetch alternative
function forLastItemAlt(array, size) {
  const arr = [];

  function getLastChunk() {
    if (arr.length === 0) {
      return null;
    }
    return arr[arr.length - 1];
  }
  for (let i = 0; i < array.length; i++) {
    let lastChunk = getLastChunk();
    if (!lastChunk || lastChunk.length === size) {
      arr.push([array[i]]);
    } else {
      lastChunk.push(array[i]);
    }
  }
  return arr;
}

// For of with last item fetch alternative
function forOfLastItem(array, size) {
  const arr = [];

  function getLastChunk() {
    if (arr.length === 0) {
      return null;
    }
    return arr[arr.length - 1];
  }
  for (const item of array) {
    const lastChunk = getLastChunk();
    if (!lastChunk || lastChunk.length === size) {
      arr.push([item]);
    } else {
      lastChunk.push(item);
    }
  }
  return arr;
}