[rare JavaScript stuff I forget all the time] #JavaScript

js.js

// null coalescings https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Nullish_coalescing
foo = foo ?? 42
foo ??= 42

// optional chaining https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Optional_chaining
dog?.name
dog?.[name]
hello?.(target)


// https://devdocs.io/dom/structuredclone
structuredClone(value)
structuredClone(value, options)

//https://devdocs.io/javascript/global_objects/array/sort
export function compare(a, b): number {
  return a.localeCompare(b)
  return a - b
}
// - <0 => sort a to an index lower than b => i.e. a comes first
// - =0, leave a and b unchanged with respect to each other, but sorted with respect to all different elements. Note: the ECMAscript standard does not guarantee this behavior, thus, not all browsers (e.g. Mozilla versions dating back to at least 2003) respect this.
// - >0, sort b to an index lower than a => i.e. b comes first
// -  must always return the same value when given a specific pair of elements a and b as its two arguments. If inconsistent results are returned, then the sort order is undefined.

///////
// https://devdocs.io/javascript/global_objects/encodeuricomponent
encodeURIComponent(location.hostname)
encodeURI(location.hostname)
    
///////
const ROOT_PROTOTYPE = Object.create(null)
const SEC = Object.create(ROOT_PROTOTYPE)

/////// loop controls
break
continue

// https://enmascript.com/articles/2019/09/20/two-exceptional-use-cases-for-the-spread-operator-you-may-not-know-of
const isDog = true;
const obj = {
    key: 'value',
    ...(isDog && { woof: true }),
}

// https://dmitripavlutin.com/javascript-array-from-applications/
Array.from(arguments)
Array.from(arrayToClone);
Array.from({length: 12}, (item, index) => index) // 
Array.from(new Set(array)) // unique items

// dedupe array with sets
Array.from(new Set([...old_base.roles, ...new_base_n.roles]).sort()
           
s = new Set(['a', 'b'])
ss = new Set([ ...s, 'c'])

/////// enhanced object literals ///////
http://www.benmvp.com/learning-es6-enhanced-object-literals/

{
  make,  // same as make: make

  // computed values now work with
  // object literals
  ['make' + make]: true,

  // Method definition shorthand syntax
  // omits `function` keyword & colon
  depreciate() {
    this.value -= 2500;
  }
}



/////// timestamp ///////
// https://stackoverflow.com/questions/221294/how-do-you-get-a-timestamp-in-javascript
+new Date()  // <-- note the + operator!
(new Date()).toISOString()

/////// errors ///////
// https://github.com/Offirmo/extended-exceptions.js
Error (standard)  <-- javascript root exception
+ EvalError       <-- Vanilla javascript exceptions
+ RangeError      <-- ...
+ ReferenceError  <-- ...
+ SyntaxError     <-- ...
+ TypeError       <-- ...
+ URIError        <-- ...

/////// chars ///////
str.charCodeAt(index)
str.codePointAt(pos)
String.fromCharCode(num1[, ...[, numN]])
String.fromCodePoint(num1[, ...[, numN]])

hexString = yourNumber.toString(16)
yourNumber = parseInt(hexString, 16)

// https://stackoverflow.com/questions/1877475/repeat-character-n-times
Array(11).join("a") // create string with 10 as "aaaaaaaaaa"
Array(10).fill('a').join('')



/////// break ///////
outer_block: {
  inner_block: {
    console.log('1');
    break outer_block; // breaks out of both inner_block and outer_block
    console.log(':-('); // skipped
  }
  console.log('2'); // skipped
}

resolution: {
  if (!_.isString(message)) {
    problems.push('invalid message')
    break resolution
  }

  let message_format: IntlMessageFormat<any>
    try {
      message_format = new IntlMessageFormat(message, locale, custom_formats)
    }
  catch (err) {
    problems.push('unable to parse message format (*)')
    underlying_error = err
    break resolution
  }

  // eventually
  try {
    formatted_msg = message_format.format(values)
  }
  catch (err) {
    problems.push('unable to compile message (*)')
    underlying_error = err
    break resolution
  }
}

if (underlying_error) ...



/////// SETS ///////

const seen_nodes = new Set()
let node = head
while(node) {
  if (seen_nodes.has(node))
    return true
  seen_nodes.add(node)
  node = node.next
}
return false



/////// REDUCE ///////
res = .reduce((acc, val) => {
  return acc + val
}, 0)
err = decorators.reduce((err, decorator) => {
  return decorator(err)
}, err)



/////// CUSTOM JS ERROR ///////

/**
 * See:
 * https://github.com/Offirmo/extended-exceptions.js/blob/master/extended_exceptions.js
 *
 * http://stackoverflow.com/questions/33870684/why-doesnt-instanceof-work-on-instances-of-error-subclasses-under-babel-node
 * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error
 *
 Objet très spécial

    https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error#Custom_Error_Types
    http://stackoverflow.com/questions/1382107/whats-a-good-way-to-extend-error-in-javascript
    http://www.ecma-international.org/ecma-262/5.1/#sec-15.11.1
    https://github.com/sindresorhus/aggregate-error
 */
function CustomException(message) {
  this.name = 'CustomException';
  this.message = message || 'XYZ will not run.';
  this.stack = (new Error()).stack;
}
CustomException.prototype = Object.create(Error.prototype);
CustomException.prototype.constructor = CustomException;

        
/////// ACCESS //////