[minor] Use indexed access to string chars

[victor-homyakov]

There is no need to split() string into array of chars: string also has indexed access

[victor-homyakov]

One of Travis CI jobs (test in browser) fails because of error in zuul: SyntaxError: Block-scoped declarations (let, const, function, class) not yet supported outside strict mode

https://travis-ci.org/github/unshiftio/yeast/jobs/663048501#L321

Might be fixed in #18

[lpinca]

Using an array seems to be faster.

const Benchmark = require('benchmark');

const suite = new Benchmark.Suite();

const string =
  '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-_';
const array = string.split('');

let result;

function randomIndex() {
  return Math.floor(Math.random() * 64);
}

suite.add('string', function() {
  result = string[randomIndex()];
  return result;
});

suite.add('array', function() {
  result = array[randomIndex()];
  return result;
});

suite.on('cycle', function(event) {
  console.log(event.target.toString());
});

suite.on('complete', function() {
  console.log('Fastest is ' + this.filter('fastest').map('name'));
});

suite.run({ async: true });

$ node index.js 
string x 69,631,394 ops/sec ±0.34% (93 runs sampled)
array x 80,212,620 ops/sec ±0.30% (91 runs sampled)
Fastest is array

[victor-homyakov]

Very interesting difference in performance. What about other JS engines?

[lpinca]

I don't know I've only run it on Node.js 13.x

[victor-homyakov]

I've added two more checks to see whether speed differences are systematic or random

const Benchmark = require('benchmark');
const suite = new Benchmark.Suite();
const string = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-_';
const array = string.split('');

let result;

function randomIndex() {
  return Math.floor(Math.random() * 64);
}

suite.add('string 1', function() {
  return string[randomIndex()];
});

suite.add('array 1', function() {
  return array[randomIndex()];
});

suite.add('string 2', function() {
  return string[randomIndex()];
});

suite.add('array 2', function() {
  return array[randomIndex()];
});

suite.on('cycle', function(event) {
  console.log(event.target.toString());
});

suite.on('complete', function() {
  console.log('Fastest is ' + this.filter('fastest').map('name'));
});

suite.run({ async: true });

Two benchmark runs in Node 8.6.0:

string 1 x 49,305,524 ops/sec ±1.02% (85 runs sampled)
array 1 x 48,975,469 ops/sec ±0.55% (90 runs sampled)
string 2 x 49,163,275 ops/sec ±1.44% (90 runs sampled)
array 2 x 48,691,671 ops/sec ±0.65% (85 runs sampled)
Fastest is string 1,string 2

string 1 x 48,392,746 ops/sec ±1.52% (87 runs sampled)
array 1 x 49,001,437 ops/sec ±0.45% (95 runs sampled)
string 2 x 50,636,402 ops/sec ±0.56% (85 runs sampled)
array 2 x 49,098,526 ops/sec ±0.97% (86 runs sampled)
Fastest is string 2

Two benchmark runs in Node 12.13.0:

string 1 x 64,548,401 ops/sec ±0.81% (92 runs sampled)
array 1 x 77,401,569 ops/sec ±0.45% (92 runs sampled)
string 2 x 63,871,694 ops/sec ±2.70% (85 runs sampled)
array 2 x 76,654,940 ops/sec ±1.11% (89 runs sampled)
Fastest is array 1,array 2

string 1 x 63,000,088 ops/sec ±1.60% (87 runs sampled)
array 1 x 76,415,302 ops/sec ±0.51% (95 runs sampled)
string 2 x 63,639,327 ops/sec ±2.86% (87 runs sampled)
array 2 x 76,791,568 ops/sec ±1.27% (92 runs sampled)
Fastest is array 1

The same benchmark for browsers: https://jsperf.com/random-array-access-vs-random-string-access/1

Ops/sec in different browsers:

Data	Chrome 80	Chrome 83	Firefox 74	Safari 13
array	68,543,368	68,946,341	221,238,676	10,146,724
string	63,945,222	66,640,438	221,776,737	10,273,448

While Firefox and Safari show similar speed for both array and string, fresh Node.js versions and Chrome browsers obviously prefer the array as the fastest structure.