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JavaScript

Introduction

  • What is JavaScript
    • JavaScript is a cross-platform, object-oriented scripting language used to make webpages interactive
    • Client-side JavaScript extends the core language by supplying objects to control a browser and its Document Object Model (DOM).
    • Server-side JavaScript extends the core language by supplying objects relevant to running JavaScript on a server.
    • node.js is a more advanced server side versions of JavaScript.
  • ECMA script
    • The ECMAScript specification is a set of requirements for implementing ECMAScript.
    • ECMAScript is a Standard for scripting languages such as JavaScript. JavaScript is a language based on ECMAScript.
    • JavaScript supports all functionality outlined in the ECMAScript specification.

Gramer and types

  • basics

    • case-sensitive
    • use Unicode character set
    • simicolon after each statement

  • declarations

    • var - local or grobal variable
    • let - block-scoped variable
    • const - block-scoped read-only constant

  • evaluate variables

    • no assigned value variable has the type undefined
    • undefined converts to false、NAN
    • null converts to 0

  • variable scope

    • var variable is either global or local in a funtion
    • let and const support block-scoped

  • variable hoisting

    • variables in JavaScript are hoisted to the top of the function or statement.
    • var are hoisted return a value of undefined.
    • let and const are hoisted but not initialized.

  • function hoisting

    • hoisted if defined using function declarations, but not hoisted if defined using function expressions

      //function declarations
function calcRectArea(width, height) {}
      //function expressions
const getRectArea = function(width, height) {}

  • constant

    • vairable is constant is not equal to the member or value of this variable is constant.

Data structures and types

  • eight types

    • seven promitives
      • Boolean
      • null
      • undefined
      • Number - An integer or floating point number.
      • Bigint - An integer with arbitrary precision.
      • String
      • Symbol
    • one other
      • object - named containers for values

  • data type conversion

    • numeric values conver to strings when +, numeric values not conver to strings when other operators

    • convert string to number

      parseInt()
      parseFloat()

literal

  • array literal

    • let array = ["1","2", 1232]

    • Array literals are also Array objects.

  • boolean literal

    • true、false
    • Boolean object is a wrapper around the primitive Boolean data type.

  • numberic literal

    • integer literals in different bases and floating-point literals in base-10.
    • 123.4 - numeric literals should be unsigned. -123.4 is a plus of - and 123.4

  • integer literal

    • Integer and BigInt literals can be written in decimal, hexadecimal, octal and binary.
    • 123456n - A trailing n suffix on an integer literal indicates a BigIntliteral.

  • float point literal

    • parts
      • An unsigned decimal integer
      • A decimal point (".")
      • A fraction (another decimal number)
      • An exponent
    • 3.1415926、3.1E+12

  • object literals

    • An object literal is a list of zero or more pairs of property names and associated values of an object, enclosed in curly braces ({}).

    • var car = { myCar: 'Saturn', getCar: carTypes('Honda'), special: sales };

    • In ES2015, object literals are extended, and it's just like more classed base object.

  • string literals

    • both ' and " is ok

    • javaScript automatically converts the string literal to a temporary String object.

    • template

      • enclosed by the back-tick (`)

      • `Hello ${name}, how are you ${time}?`