JavaScript¶

Strings¶

Template Literals¶

Feels like Python f"formatted_string"

myTag`A${1}B${2}C${3}D${4}E${5}F`;

function myTag(strings, ...args) {
    console.log(strings); // ['A', 'B', 'C', 'D', 'E', 'F']
    console.log(args); // [1,2,3,4,5]
    return strings;
}

JS Regex¶

[[python-regex]]

The dot in RegExp doesn't match all characters in JS

`RegExp.test()` -> boolean¶

console.log(/^([a-z0-9]{5,})$/.test('abc1')); // false

`String.match()` vs `RegExp.exec()`¶

regex - match Vs exec in JavaScript

match can do all at once with global flag

console.log("[22].[44].[33].".match(/\d+/g));
// [ '22', '44', '33' ]

without global flag, will find the first

`RegExp.exec()`¶

has a nice syntax for looping with capturing groups?

One at a time

// NEED THE global flag
myRegexp = /\[(\d+)\]/g

while (result = myRegexp.exec("[22].[44].[33].")) {
    console.log(result, myRegexp.lastIndex);
// [
//  '[33]',
//  '33',
//  index: 10,
//  input: '[22].[44].[33].',
//  groups: undefined
//  ] 14
}

Numbers¶

NaN¶

Number.isNaN("a"); // false
isNaN("a"); // true

Number.isNaN(Number(input)) === isNan(input);

Functions¶

kwargs (obj --> params)¶

const sum = (a, b) => a + b;

How do I pass this in args = {a: 1, "1": 2}?

Can't destructure

// sum(args)  // a = args, b = undefined
// sum(...args)  // TypeError: Found non-callable @@iterator

Solution: get the object values as an array¶

// order: [Does JavaScript guarantee object property order?](https://stackoverflow.com/a/23202095)
// 1. integer keys (like "11")
// 2. string keys
// 3. Symbol keys
argValues = Object.values(args); // [2,1]
c = sum(...argValues);
console.log(c);

Importing¶

CommonJS vs AMD

at the start, commonJS sucked on browsers

AMD was used because people had to use it

you explicitly declare your dependencies for each function/module

now, neither are the best

Use a build tool

Import a package in the dev tools¶

Dynamic imports

const { default: Confetti } = await import('https://cdn.skypack.dev/canvas-confetti');

Symbols¶

Why symbols¶

All symbols are unique
For fully unique keys
private properties
- (PITA to access)

Unique sentinel values, identity checks, and when to use object() instead of None

React uses symbols

Last update: 2023-04-24