Course Overview

Overview of history of the JavaScript language

History of JavaScript

Overview of the relationship between JavaScript and Java

JavaScript vs Java

Overview of how JavaScript is evolved as a programming language

How is it evolved?

Overview of how we can track upcoming features in the JavaScript language

How to track upcoming features?

Overview of how the ECMAScript is versioned

How is ECMAScript versioned?

Explanation of whether JavaScript is interpreted or a compiled language

Is it interpreted or compiled?

Explanation of how JavaScript is executed

How is it executed?

Execution Context

Explanation of what is a callstack and how it is used in JavaScript

Callstack

Overview of memory management in JavaScript

Memory

What is JavaScript

What is hoisting?

Explanation of common misconception about hoisting in JavaScript

Misconception about hoisting

Hoisting

What is scope?

Explanation of global scope in JavaScript

Global scope

Explanation of function scope in JavaScript

Function scope

Block scope

Explanation of module scope in JavaScript

Module scope

Scope chain

Scope

What is coercion?

Diving into inner details of  coercion in JavaScript

Deeper look at coercion

Explanation of what abstract operations are and common types of abstract operations in JavaScript

Abstract operations

Explanation of how abstract or loose equality works in JavaScript

Abstract equality operator

Explanation of how the addition operator works in JavaScript

Addition operator

Explanation of how relational operators work in JavaScript

Relational operators

Coercion exercise for testing and practicing the knowledge learned in this module

Coercion exercise

Coercion

What is a closure?

Explanation of a common misconception about closures in JavaScript

Misconception about closures

Explanation of the problem of closures inside loops and how to fix it

Closures inside loops

Explanation of closures can be used to hide data

Data hiding using closures

Closures

What is prototypal inheritance?

Prototype chain

__proto__ property

Explanation of how we can create objects with custom prototypes in JavaScript

Custom prototypes

Explanation of how prototype chain is set with ES6 classes

ES6 classes and prototypes

Prototypes

Explanation of this keyword in JavaScript

What is this?

Explanation of how "this" works inside arrow functions

Arrow functions and "this"

Explanation of how value of "this" can be set explicitly

Explicitly binding "this"

globalThis

Summarizing "this"

'this' keyword

What is a symbol?

Explanation of why symbols were added in JavaScript

Why symbols?

Symbols and privacy

Explanation of global symbols in JavaScript

Global symbols

Explanation of what well-known symbols are in JavaScript

Well-known symbols

Symbol

Overview of asynchronous behavior of JavaScript

Overview

Overview of how callbacks help us write asynchronous code in JavaScript

Callbacks

Event loop

Promise

Explanation of promise chaining in JavaScript

Promise chaining

Explanation of some static methods of promises and their use cases

Use cases for static Promise methods

Explanation of async-await syntax in JavaScript

async await

Explanation of microtasks, how they are processed, and how they are linked to promises

Microtasks

Explanation of common anti-patterns to avoid when using promises in JavaScript

Promise anti-patterns

Asynchronous JavaScript

Explanation of what is an iterator in JavaScript

Iterators

Explanation of what is a generator in JavaScript

Generators

Explanation of how we can create asynchronous iterators in JavaScript

Asynchronous iterators

Explanation of how we can create asynchronous generators in JavaScript

Asynchronous generators

Iterators and Generators

Overview of what is debugging and different ways to debug JavaScript

Debugging

Overview of using the "debugger" statement to debug JavaScript

Debugger statement

Overview of using the breakpoints in browser developers' tools to debug JavaScript

Breakpoints in browser

Overview of using the VS Code debugger to debug JavaScript

VS Code debugger

Debugging JavaScript

Final thoughts and advice regarding how to continue the exciting journey of learning JavaScript

Conclusion

Wrap up

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Become a confident JavaScript pro by unraveling the most challenging aspects of the language. With easy-to-understand explanations and code examples, you’ll gain a deeper and solid understanding of JavaScript's most complex features.

Advanced JavaScript Unleashed is for beginner and intermediate developers alike, who want to elevate their JavaScript skills and become senior engineers by gaining a deeper understanding of the core topics of the language.

Advanced JavaScript Unleashed

The function scope refers to the area of the code within the function body. The function scope starts from the opening curly parenthesis of the function body and ends before the closing curly parenthesis. Declarations inside the function scope are limited to that function's scope and cannot be directly accessed by the code outside that function.

Declarations inside a nested scope can "shadow" the declarations with the 

 name in the outer scope. This is referred to as "shadowing declaration" or simply "shadowing."

let hobby = "reading";

function printHobbies() {
  const hobby = "traveling";
  console.log(hobby); // traveling
}

printHobbies();

It is generally not ideal to shadow other declarations because that can reduce the readability of the code. It could also make it impossible for code inside the nested scope to access the shadowed declarations. Consider the following code example:

let prefix = ">";

function log(logLevel, msg) {
  let prefix = ":::";
  console.log(`${prefix} ${logLevel} : ${msg}`);
}

log("debug", "error caught"); // ::: debug : error caught

In the code example above, we have shadowed the 

 variable declared in the global scope, and the code inside the 

 function is unable to access the global 

 declarations in the global scope are added as properties on the 

It is a common misconception that the function parameters are defined in the function's local scope or that the parameters behave as if they are defined in the function's local scope, but that is not always true.

First, we need to differentiate between "simple" and "non-simple" parameter lists. If the function parameters are defined in such a way that they use ES2015+ features like 

 parameters; if the parameters don't use any of these features, they are considered to be 

function simpleParameters(val1, val2) {
  // code...
}

function nonSimpleParameters(val1 = 12, ...restParams) {
  // code...
}

If the parameters are simple, they behave like they are declared in the function's local scope, but if the parameters are non-simple, they are declared in their own scope. Non-simple parameter scope can be thought of as between the function scope and the scope containing the function.

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title: Function scope
description: Explanation of function scope in JavaScript
isPublicLesson: false
useMdx: true
code: https://gitlab.com/fullstackio/books/newline-course-apps/advanced-javascript-unleashed-app/-/tree/main/module_03/lesson_03.03
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The function scope refers to the area of the code within the function body. The function scope starts from the opening curly parenthesis of the function body and ends before the closing curly parenthesis. Declarations inside the function scope are limited to that function's scope and cannot be directly accessed by the code outside that function.

## Shadowing declarations

Declarations inside a nested scope can "shadow" the declarations with the _same_ name in the outer scope. This is referred to as "shadowing declaration" or simply "shadowing."

Consider the following code example:

```js
let hobby = "reading";

function printHobbies() {
  const hobby = "traveling";
  console.log(hobby); // traveling
}

printHobbies();
```

Here's a Replit of the code above:

<ReplitEmbed src="https://replit.com/@newlineauthors/function-scope-example1"/>

The variable `hobby` inside the function is shadowing the `hobby` variable declared in the global scope.

It is generally not ideal to shadow other declarations because that can reduce the readability of the code. It could also make it impossible for code inside the nested scope to access the shadowed declarations. Consider the following code example:

```js
let prefix = ">";

function log(logLevel, msg) {
  let prefix = ":::";
  console.log(`${prefix} ${logLevel} : ${msg}`);
}

log("debug", "error caught"); // ::: debug : error caught
```

Here's a Replit of the code above:

<ReplitEmbed src="https://replit.com/@newlineauthors/function-scope-example2"/>

In the code example above, we have shadowed the `prefix` variable declared in the global scope, and the code inside the `log` function is unable to access the global `prefix` variable.

:::note

Recall that the `var` declarations in the global scope are added as properties on the `window` object. So, if the global `prefix` variable was declared using the `var` keyword, we could have used `window.prefix` to access the shadowed variable.

:::

## Function parameter scope

It is a common misconception that the function parameters are defined in the function's local scope or that the parameters behave as if they are defined in the function's local scope, but that is not always true.

First, we need to differentiate between "simple" and "non-simple" parameter lists. If the function parameters are defined in such a way that they use ES2015+ features like [Default parameters](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Default_parameters), [Destructuring](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment), or [Rest parameters](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/rest_parameters), such parameters are considered to be **non-simple** parameters; if the parameters don't use any of these features, they are considered to be **simple** parameters.