JavaScript Kata #37: Convert a String to a Number!

By YayoDrayber | Learn To Code With Me | 19 Sep 2022

If you missed the introductory post, it's here. For a list of previously solved katas, please refer to the bottom of this page.

If this is your first time seeing my post, please note - these katas are probably randomly assigned per user so please don't go into Codewars thinking we will have exactly the same user experience, I am just posting these in the order that I got them.

Kata #37

DESCRIPTION:

Note: This kata is inspired by Convert a Number to a String!. Try that one too.

Description

We need a function that can transform a string into a number. What ways of achieving this do you know?

Note: Don't worry, all inputs will be strings, and every string is a perfectly valid representation of an integral number.

Examples

"1234" --> 1234
"605"  --> 605
"1405" --> 1405
"-7" --> -7

Starting code:

const stringToNumber = function(str){
  // put your code here
  return null;
}

My attempt:

const stringToNumber = str => Number(str)

Rank #1 in 'Best Practice':

var stringToNumber = function(str){
  return parseInt(str);
}

Rank #2:

var stringToNumber = function(str){
  // put your code here
  return Number(str);
}

Rank #3:

var stringToNumber = function(str){
  return +str;
}

Rank #4:

const stringToNumber = str => Number(str)

Rank #5:

var stringToNumber = Number;

And in rank #6 we can see a troll that goes by a.vadim:

const ways = [
  s => +s,
  s => s++, // why does it work?
  s => s--,
  s => ++s - 1,
  s => --s + 1,

  s => s * 1,
  s => s - 0,
  s => s / 1,
  s => s - '',
  s => s ** 1,
  s => s % Infinity,

  s => ~~s,
  s => s & -1,
  s => s | 0,
  s => s ^ 0,
  s => s << 0,
  s => s >> 0,
  s => s | s,
  s => s & s,

  s => ~s ^ -1,
  s => ~s ^ ~0, // ~0 = -1
  s => ~(s ^ -1),
  s => s * !!s,

  s => -1 * (~s + 1) || 0, // -1 * 0 = -0
  s => -(~(s >>> 0) + 1) || 0,

  Number,
  parseInt,
  parseFloat,
  
  s => Number(s),
  s => parseInt(s),
  s => parseFloat(s),

  s => Math.floor(s),
  s => Math.round(s),
  s => Math.ceil(s),
  s => Math.min(s),
  s => Math.max(s),
  
  Math.floor,
  Math.round,
  Math.ceil,
  Math.min,
  Math.max,

  s => eval(`+ ${s}`), // a space is needed
  s => eval('+ ' + s), // for cases like eval(+ +12345)

  s => [...s]
    .slice(+(s[0] == '-' || s[0] == '+')) // remove the sign, if present
    .reduce((acc,x) => +x + acc * 10)
    * (s[0] == '-' ? -1 : 1),
  s => [...s]
    .slice(+(s[0] == '+')) //remove +, if present
    .reverse()
    .reduce((acc,x,i) => x == '-' ? -acc : acc += x * 10 ** i, 0),
  s => ways[~~(Math.random() * ways.length)](s)
];

// And now we will use all the methods in a row

const checkThemAll /* © Mylene Farmer */ = (acc, x) => acc === x ? x : NaN;
const stringToNumber = str => ways.map(fn => fn(str)).reduce(checkThemAll);

That's it for Kata #37, stay tuned for more katas to be solved!

Link to Kata #1: Square(n) Sum

Link to Kata #2: Convert a Number to a String

Link to Kata #3: DNA to RNA Conversion

Link to Kata #4: Remove First and Last Character

Link to Kata #5: MakeUpperCase

Link to Kata #6: Total amount of points

Link to Kata #7: A Needle in the Haystack

Link to Kata #8: Sum of positive

Link to Kata #9: Basic Mathematical Operations

Link to Kata #10: Beginner - Reduce but Grow

Link to Kata #11: Square Every Digit