Javascript Typescript - ayaohsu/Personal-Resources GitHub Wiki

Enumeration

  • enum, with no exception, is an object in javascript
  • enum Side { BUY, SELL} is an object of:
{
    BUY: 0,
    0: "BUY",
    SELL: 1,
    1: "SELL"
}

Template literals

  • string literals allowing embedded expressions.
 `string text ${expression} string text`
  • enclosed by the back-tick instead of double or single quotes.
  • [FYI] expression can be a literal value (a string or a number), a variable, a built-in value

Javascript Loop

  • for loop for (statement 1; statement 2; statement 3) { code block to be executed }

  • forEach Array prototype array.forEach(function(currentValue, index, arr))

  • for of for (variable of iterable) { statement }

Three dots

  • rest parameters: if the last parameter is prefixed with ..., it becomes an array whose elements are supplied by the actual arguments passed to the function
function multiply(multiplier, ...theArgs) {
  return theArgs.map(function(element) {
    return multiplier * element;
  })
}

  let multiplication = multiply(5, 3, 2, 7);

  • theArgs is treated as an array

  • spread syntax: to expand an array (or any iterable) to places where zero or more arguments are expected

let dateFields = [1989, 6, 7];
let date = new Date(...dateFields);

Regular Experssions

  • Patterns used to match charater combinations in strings
let re0 = /abc/;
let re1 = new RegExp('abc');
  • Modifiers: give the property of the search; ex: i: case-insensitive, g: global search (find all matches rather than stopping at the first match)
let re0 = /abc/g;
let re1 = new RegExp('abc', i);

  • \: Non-special <-> Special

  • ^: Matches beginning of input; $: End of input

  • *: Matches the preceding expression 0 or more times. Equivalent to {0,}

  • +: Matches the preceding expression 1 or more times. Equivalent to {1,}

  • \w: Any alphanumeric character, including the underscore. Equivalent to [A-Za-z0-9\]

  • \s: Matches both space character and tab

  • \t: Matches tab

  • When finding out whether a pattern is found in a string, use test or search

let found = re0.test('abbbc');  // this should return false

Object Literal for ES6

  • Object keys can be dynamically assigned in ES6 by placing an expression in [ square brackets ].
const key = "one";
let object = {
  [key]: 1,
  "two": 2
}

// obj.one = 1, obj.two = 2

Understanding "this"

https://javascriptissexy.com/understand-javascripts-this-with-clarity-and-master-it/