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Javascript Index#

  • string, number, boolean, array, object, null, undefined

DOM Event#

- event capturing, Target phase, event bubbling, event delegation- event.target, event.target.value, event.target.closest, e.target.className, e.target.id, e.target.innerHTML- event.stopPropagation, event.stopImmediatePropagation, event.preventDefault(),- elem.addEventListener(..., true)- onchange, onclick, onmouseover, onload, onkeydown
  • Abortcontroller and symbol; cancelling the api request
  • Throttling and debouncing
  • asynchronous programming, callback and promises, callback hell, error callback
  • closure, hoisting
  • function, arguments.length, anonymous function, IIFE (use of it in singleton in vanilla js);
  • lexical, functional and block scope
  • event queue, event-loop, call stack, single threaded, macro-tasks(apicalls, setTimeout, mouse-event, script tag), micro-tasks(process.nextTick, promises - higher priority),
  • type=module in script tag (import/export, deferred execution, module scoped variables)
  • call, bind, apply (how .apply is used when num of arguments passed is uncertain and you have to write a wrapper function)
    • func.apply(this, [...args, callback]);
  • method chaining, currying,
  • generators, yield

Typescript#

  • static type checking at compile time
  • TypeScript decorators are functions that can be used to modify or add metadata to classes, methods, or properties.
  • Generics interface e.g interface myInterface<T>
  • readonly : The readonly modifier can be used to create arrays that cannot be modified after initialization.
const arr: readonly number[] = [1, 2, 3]arr.push(4) // throws errorarr[1] = 6 // throws errorconsole.log(arr[0]) // prints 1
const obj: { readonly [key: string]: any } = { a: 1, b: 2 }obj.a = 1 // throws error
  • keyof : obtain the union type of all possible property names of a given type.
type Person = {  name: string  age: number  address: string}
type PersonKey = keyof Person // "name" | "age" | "address"
  • Declaration files (.d.ts) provide type information for existing JavaScript code, allowing TypeScript to understand the types used in external libraries. Definition files are typically generated by tools like DefinitelyTyped.
  • Enums, and what are "const enums"
enum Color {  Red,  Green,  Blue}let color: Color = Color.Green
  • "strict mode" in TypeScript : ncludes options like strictNullChecks, strictFunctionTypes
  • "conditional imports" in TypeScript
if (condition) {  import("moduleA").then((moduleA) => {    // Use moduleA  })}

Document methods#

- document.querySelector(".className"),- document.querySelector("#idName"),- document.getElementById('id_name'),- document.getElementsByClassName('className')- document.cookie

  • Ecmascript

    • ES5(2009) - useStrict, JSON.stringify, JSON.parse,
    • ES6(2015) - Promises, let, const, template literal, arrow function (self = this), class, super(),constructor,extends, rest and spread. default param, destructuring,generators (function*)
    • ES7(2017) - async await and equivalent promise conversion

  • Object

    • Object.keys, Object.values, for(const of )
    • Object.freeze(), Object.seal(), Object.isFrozen(), Object.isSeal()
    • Object.prototype.hasOwnProperty
    • Object.create()
    • Prototype, constructor, proto, Object.create(), prototype.constructor (function constructor), instanceof
    • object.hasOwnProperty(property)

  • Array

    • arr.sort((a,b)=> a-b);
    • array.filter().map().join("")

Promise#

- promise.all(), promise.race(), .resolve(), .reject(), callback- state of promise : pending, fulfilled, rejected- new Promise((reolve, reject)=> {})- Difference between myPromise.then(result => {}, err => {}) and myPromise.then(result => {}).catch(err => {});
  • ways of creating an object in JS
  • data types in JS - string, number, boolean, object, array, null, undefined
  • string.reverse().split("").includes().trim()
  • AJax calls : XMLHttpRequest and fetch API (modern version)
  • higher order functions (e.g map, filter, foreach etc.)
  • JSONP (JSON with Padding) - hack for handling cors issue
  • Host objects(provided by browser or run time env like node.js) vs native objects (provided by language)
  • Debugging
    • chrome devtools
    • debugger statement
    • console.log
  • CommonJS abd Asynchronous Module Definition (AMD)
  • DOMContentLoaded and load event
  • UA string (user agent string)
  • Feature Detection