JavaScript

[DanKim0213]

JavaScript

Javascript concept hierarchy I referred to MDN javascript guide

Hierarchy

TODO list

• [ ] What is Closure?
• [ ] Null vs Undefined
• [ ] JavaScript: The Good Parts by Douglas Crockford
• [ ] How JavaScript Works by Douglas Crockford
• [ ] Blog Nordic.js 2014 • Douglas Crockford - The Better Parts
• [ ] Blog The Next Programming Language - Douglas Crockford - code::dive 2022

[DanKim0213]

Things to complement

• Module
• Class
• Collections
• Execution Context Stack
• Questions

[DanKim0213]

statement vs declaration "You can see declarations as "binding identifiers to values", and statements as "carrying out actions"."

[DanKim0213]

Hoisted with let or const variables?

"All declarations (var, let, const, function, function*, class) are "hoisted" in JavaScript."

JavaScript has the following kinds of scopes:

• Global scope: The default scope for all code running in script mode.
• Module scope: The scope for code running in module mode.
• Function scope: The scope created with a function.

In addition, variables declared with let or const can belong to an additional scope:

• Block scope: The scope created with a pair of curly braces (a block).

References

• Are variables declared with let or const hoisted?
• Hoisting in JavaScript with let and const – and How it Differs from var
• Scope

[DanKim0213]

Arrow function

MDN TODO:

setTimeout in MDN

class Hello {
  constructor() {
    this.name = "semi";
  }

  bloom() {
    // this.declare();
    // by default, `this` within setTimeout is globalThis.
    // setTimeout(this.declare.bind(this), 1000);
    setTimeout(() => this.declare(), 1000);
  }

  declare() {
    console.log("hoi hoi", this.name);
  }
}

const hello = new Hello();
hello.bloom();

Arrow function expressions should only be used for non-method functions because they do not have their own this. Let's see what happens when we try to use them as methods:

TODO: However, because it is a closure, not the function's own binding, the value of this will not change based on the execution context.

Arrow function properties are often said to be "auto-bound methods", because the equivalent with normal methods is:

[DanKim0213]

Event Loop

According to MDN - Event Loop:

JavaScript has a runtime model based on an event loop, which is responsible for executing the code, collecting and processing events, and executing queued sub-tasks.

https://www.javascripttutorial.net/javascript-event-loop

[DanKim0213]

Closures

[DanKim0213]

What is JavaScript

https://www.javascripttutorial.net/what-is-javascript/ https://www.javascripttutorial.net/javascript-event-loop/

JavaScript is a single-threaded programming language. This means that JavaScript can do only one thing at a single point in time.

[DanKim0213]

New keyword

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/new#description