/JS_understanding-the-weird-parts

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Javascript: Understanding the Weird Parts

Javascript Vocabulary/Terms:

Don't be afraid of big words. It's just vocabulary!

  • Syntax Parser

    • A program that reads your code and determines what it does and if its grammar is valid.
    • Your code isn't magic. Someone else wrote a program to translate it for the computer. These programs are commonly known as compilers or translators.

  • Lexical Environment

    • The physical location of something in your code.
    • 'Lexical' means 'having to do with words or grammar'. A lexical environment exists in programming languages where the location of what you write is important.

  • Execution Context

    • A wrapper to help manage the code that's running.
    • There are lots of lexical environments. Which one should be running is managed by execution contexts. It can contain things beyond what has been written in your code.

  • Name/Value Pair

    • A name which maps to a unique value.
    • The name in question may be defined more than once, but can only have one value in any given execution context. That value may itself be additional name/value pairs.

  • Object

    • A collection of name/value pairs.
    • The simplest possible definition when talking about Javascript. Objects may be handled differently in other programming languages.

  • Hoisting

    • Memory space set aside in the execution context for variables and functions
    • Variables are stored and set as "undefined"; functions are stored in memory in their entirety.
    • Hoisting occurs prior to the execution phase in a given execution context.

  • Word

    • Definition
    • More Detail

  • Word

    • Definition
    • More Detail

Conceptual Asides

Syntax Parsers, Lexical Environments & Execution Contexts

Syntax Parsers:

Syntax parsers are programs written to translate your code for the computer. This takes place in the intermediate step between the time your code is executed and the actual end result.

Lexical Environment:

Where you write certain pieces of your code matters in certain programming languages. In these languages, the lexical environment is crucial in order for the compiler to properly translate your code.

This isn't the case for all programming languages.

Execution Context:

Since there are many different lexical environments, an execution context helps manage which lexical environment is currently running.

The Global Execution Context:

The base execution context is called a "global" execution context. This simply means that it's not inside a function. Two key things are created by JS in this global context:

  • Global object
  • Global variable "this"

When the global execution context is created in a browser window, the global object is the browser window (an object called "window") and "this" simply refers to that object. Therefore, we can say that the global object "window" === "this" in the global execution context.

If a function or a variable is defined in this global context, they are assigned to the global object. In the case of a browser, they are assigned to the global object "window".

Each execution context is set up in 2 phases:

  • Creation Phase
    • Global Object
    • "this"
    • Outer Environment
    • Memory space for variables and functions (Hoisting)
  • Execution Phase +

Name/Value Pairs & Objects

A name/value pair is a name that maps to a value. The name in question may be defined more than once, but can only have one value in any given execution context. That value may itself be additional name/value pairs.

Example:

var address = '100 Main St.'

In this example, the variable address is the name, and the string '100 Main St.' is the value. In Javascript one of the main ways name/value pairs are used is with objects.

Example:

var address = {
  Street: 'Main',
  Num: 100
  Apartment = {
    Floor: 3,
    Num: 301
  }
}

Don't make objects more complicated than they are! Objects are simply collections of name/value pairs.