JavaScript Magic cover image

JavaScript Magic

updated over 5 years ago

Imperative vs. Recursive vs. Functional

credit: markus-spiske-197281-unsplash.jpg

[ Work-in-progress ]

// Imperative: The Fastest ( + very simple, no new pointers or excess allocs ):
function fib(n) {
  var a = 1, b = 1, c = 0;
  for(var i = 1; i < n-1; ++i) {
    c = a + b;
    a = b;
    b = c;
  return b;

// Recursive: (FIREFOX or BABELJS Only) ES6 function definition with
//  parameter defaults used to set initial (internal/recursive) values
function fib(n, current=0, a=1, b=1, c=0) {
  c = a + b;
  a = b;
  b = c;
  return current >= n ? b : fib(n, current, a, b, c);

// Text-book-Bad Example - poor function scope w/ multiple mutable external values
function fib(n) {
  if (!arr) { var arr = [1,1]; n=n-2; };// Bad
  if (n===-1) {return [arr[0]];}
  if (n===0) {return arr;}
  var proc = function() {
    arr.push(arr[arr.length-1] + arr[arr.length-2]);
    return (n===0 ? arr : proc());
    // Bad: inner recursive function not needed, hint: variables used are from parent function scope
  var ans = proc();
  return ans[ans.length-1];

Promises: Awesome!

// Example Using bluebird Promises and it's
var Promise = require('bluebird'),
    fs = Promise.promisifyAll(require('fs')),
    less = Promise.promisifyAll(require('less'));

function writeFileData(data) {
  return fs.writeFileAsync('/tmp/output.css', data);
// Bluebird makes something like this perhaps uncomfortably simple and succinct:
fs.readFileAsync('./style.less') // Call promisified readFile()
  .then(less.renderAsync)         // Hand off to less.render
  .then(writeFileData);      // Function to recieve the css contents (1st parameter)
  1. While, native ES6 Promises are great, I prefer the robust Bluebird Promise Library.
  2. Library or not, modern browsers have supported Promise for years.
  3. Promises can be utilized without crazy patterns - implicit deferred is preferable.
  4. $q just sucks just use bluebird, see above.
  5. Worth mentioning: Bluebirds Benchmarks are best-case tests, so take note if doing crazy fancy promise chains

Java vs JavaScript

Rate Limiting / Debouncing / Throttling

  1. In JavaScript David Walsh implemented debounce in less than 20 lines!
  2. In Java, JDebounce, an library which is a lot more complicated, at ~500+ lines.
  3. _ Comparing the two: _
  4. The JavaScript is fast & uses first-class functions to achieve brilliant simplicity.
  5. Whereas the Java has many more moving parts, annotations are used to apply behaviour at compile-time, and there’s a ton of XML, just for funsies!

Unless otherwise noted, copyright ©2014-2021 Dan Levy.