.separate-js

Like .filter(), but instead of copying the original array, this is the modifying one.

I just wonder why Javascript does not have a prototype function for modifying the original array. So, I made it myself. See function.js

My motivation for made this prototype function

.filter() is copying the original array. So, my concern is that if the array has 100k elements, .filter() will increase memory usage for elements that fulfill the condition.

Example: Let's imagine that we want to filter users by age. And we have 100k users.

// functions for show memory usage
function measureMemoryUsage() {
  const memoryUsage = process.memoryUsage();
  console.log('Memory usage:');
  console.log(`  - RSS: ${formatBytes(memoryUsage.rss)}`);
  console.log(`  - Heap Total: ${formatBytes(memoryUsage.heapTotal)}`);
  console.log(`  - Heap Used: ${formatBytes(memoryUsage.heapUsed)}`);
  console.log(`  - External: ${formatBytes(memoryUsage.external)}`);
}

function formatBytes(bytes) {
  const sizes = ['Bytes', 'KB', 'MB', 'GB', 'TB'];
  if (bytes === 0) return '0 Byte';
  const i = parseInt(Math.floor(Math.log(bytes) / Math.log(1024)));
  return Math.round(bytes / Math.pow(1024, i), 2) + ' ' + sizes[i];
}

// functions for simulation
function generateRandomString(length) {
  const characters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
  let result = '';
  for (let i = 0; i < length; i++) {
    result += characters.charAt(Math.floor(Math.random() * characters.length));
  }
  return result;
}

function generateRandomNumber(min, max) {
  return Math.floor(Math.random() * (max - min + 1)) + min;
}

// the prototype function
Array.prototype.separate = function (callback) {
  const arr = []

  if (typeof callback !== 'function') throw new Error('.separate() needs a callback!')

  for (let i = 0; i < this.length; i++) {
    if (callback(this[i])) {
      arr.push(this.splice(i, 1)[0])
      i -= 1
    }
  }

  return arr
}


const users = Array.from(Array(100_000), () => {
  return {
    name: generateRandomString(10), // simulate name
    age: generateRandomNumber(1, 100) // simulate age
  }
});

// const adultUsers = users.filter(user => user.age >= 21)
// const adultUsers = users.separate(user => user.age >= 21)

measureMemoryUsage();

On my OS, users.filter used a total memory of 52 MB, while users.separate used a total memory of 35 MB.

But yeah, this prototype function is slower than .filter(). I need to change the algorithm, or something as simple as using worker maybe(?).