const numbers = [1,2,3,4,5]
[first, second, ...others] = numbers

const numbers = [1,2,3,4,5]
const sum = (a,b,c,d,e) => a+b+c+d+e
const sum = sum(...numbers)

const {first, second, ...others } = {first: 1,second: 2,third: 3,fourth: 4,fifth: 5}
first //1
second //2
others // {third: 3,fourth: 4,fifth: 5 }

const items = {first, second, ...others }
items //{ first: 1, second: 2, third: 3, fourth: 4, fifth: 5 }

Promise.prototype.finally()

fetch('file.json')
    .then(Data => data.json())
    .catch(error => console.log(error))
    .finally(() => console.log('finished'))

Regular Expression improvements

/Roger(?=Waters)/
/Roger(?= Waters)/.test('Roger is my dog') //false
/Roger(?= Waters)/.test('Roger is my dog and Roger Waters is a famous musician') //true

/Roger(?!Waters)/
/Roger(?! Waters)/.test('Roger is my dog') //true
/Roger(?! Waters)/.test('Roger Waters is a famous musician') //false

/(?<=Roger) Waters/
/(?<=Roger) Waters/.test('Pink Waters is my dog') //false
/(?<=Roger) Waters/.test('Roger is my dog and Roger Waters is a famous musician') //true

/(?<!Roger) Waters/
/(?<!Roger) Waters/.test('Pink Waters is my dog') //true
/(?<!Roger) Waters/.test('Roger is my dog and Roger Waters is a famous musician') //false

Unicode Property Escapes \p{...} and \P{...}

/^\p{ASCII}+$/u.test('abc') //✅
/^\p{ASCII}+$/u.test('ABC@') //✅
/^\p{ASCII}+$/u.test('ABC۽❌

/^\p{ASCII_Hex_Digit}+$/u.test('0123456789ABCDEF') //✅
/^\p{ASCII_Hex_Digit}+$/u.test('h') //❌

/^\p{Lowercase}$/u.test('h') //✅
/^\p{Uppercase}$/u.test('H') //✅
/^\p{Emoji}+$/u.test('H') //❌
/^\p{Emoji}+$/u.test('۽ ۽✅

/^\p{Script=Greek}+$/u.test('ελληνικά') //✅
/^\p{Script=Latin}+$/u.test('hey') //✅

Named capturing groups

const re = /(?\d{4})-(?\d{2})-(?\d{2})/
const result = re.exec('2015-01-02')
// result.groups.year === '2015';
// result.groups.month === '01';
// result.groups.day === '02';

The s flag for regular expressions

/hi.welcome/.test('hi\nwelcome') // false
/hi.welcome/s.test('hi\nwelcome') // true

Coding Style

• The Google JavaScript Style Guide
• The AirBnb JavaScript Style Guide

• Always use the latest ES version. Use Babel if old browser support is necessary.
• Indentation: use spaces instead of tabs, indent using 2 spaces.
• Semicolons: don't use semicolons.
• Line Length: try to cut lines at 80 chars, if possible.
• Inline Comments: use inline comments in your code. Use block comments only to document.
• No dead code: Don't leave old code commented, "just in case" it will be useful later. Keep only the code you need now, version control/you notes app is meant for this.
• Only comment when useful: Don't add comments that don't help understand what the code is doing. if the code is self-explaining through the use of good variable and function naming, and JSDoc function comment, don't add a comment
• Variable declarations: always declare variables to avoid polluting the global object. Never use var . Default to const, only use let if you reassign the variable.
• Constant: declare all constant in CAPS. Use _ to separate words in a VARIABLE_NAME.
• Functions: use arrow functions unless you have a specific reason to use regular functions, like in object methods or constructors, due to how this works. Declare them as const, and use implicit returns if possible
  

  const test = (a, b) => a + b
  const another = a => a + 2

  
  Feel free to use nested functions to hide helper functions to the rest of the code
• Names: function names, variable names and method names always start with a lowercase letter (unless you identify them as private, read below), and are camelCased. Only constructor functions and class names should start capitalized. if you use a framework that requires specific conversations, change your habits accordingly. File names should all be lowercase, with word separated by -.
• Statement-specific formats and rules:
  If
  

  if (condition) {
      statements
  }
  if (condition) {
      statements
  } else {
      statements
  }
  if (condition) {
      statements
  } else if (condition) {
      statements
  } else {
      statements
  }

  
  For
  Always initialize the length in the initialization to cache it, don't insert it in the condition. Avoid using for in except with used in conjuction with .hasOwnProperty(). Prefer for of.
  

  for (initialization; condition; update) {
      statements
  }

  
  While
  

  while (condition) {
      statements
  }

  
  do
  

  do {
      statements
  } while (condition);

  
  switch
  

  switch (expression) {
    case expression:
      statements
    default:
  statements
  }

  
  try
  

  try {
      statements
  } catch (variable) {
      statements
  }
  try {
      statements
  } catch (variable) {
      statements
  } finally {
      statements
  }



• Whitespace: use whitespace wisely to improve readability: put a whitespace after a keyword followed by a ( ; before 7 after a binary operation n ( + , - , / , * , && ..); inside the for statement, after each ; to separate each part of the statement; after each ,.
• New lines: use newlines to separate blocks of code that perform logically related operations.
• Quotes favor single quotes ' instead of double quotes ". Double quotes are a standard in HTML attributes, so using single quotes helps remove problem when dealing with HTML strings. Use template literals when appropriate instead of variable interpolation.