Understanding JavaScript Basics

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Questions and Answers

Which method is used to add an element to the end of an original array?

.shift

.concat

.push (correct)

.pop

What does the .map method primarily do to an array?

Creates a new array computed from the original (correct)

Adds elements to the beginning of the array

Mutates the original array

Filters the original array based on a condition

Which method can be used to determine if an array includes a specific value?

.some

.filter

.includes (correct)

.slice

Which array method is used to reduce the array to a single value?

.reduce Signup and view all the answers

If you want to remove the last element from an array, which method should you use?

.pop Signup and view all the answers

What is the function of the .filter method?

Creates a new array based on a test condition Signup and view all the answers

Which of the following methods can flatten an array?

.flat Signup and view all the answers

Which method is used to merge two or more arrays?

.concat Signup and view all the answers

What describes a characteristic of high-level programming languages?

Abstract away complex operations Signup and view all the answers

What is meant by 'garbage-collected' in programming?

Memory is automatically managed and cleaned Signup and view all the answers

Which of the following statements correctly describes interpreted languages?

They translate code into machine language at runtime Signup and view all the answers

In the context of multi-paradigm languages, which approach allows for structuring and directing coding style?

Programming paradigms Signup and view all the answers

Which of the following features indicates that a language supports first-class functions?

Functions can be assigned to variables Signup and view all the answers

What does the non-blocking event loop in JavaScript indicate about its execution model?

It allows asynchronous task handling Signup and view all the answers

In what scenario would prototypal object-oriented programming be advantageous?

For dynamic and reusable object instances Signup and view all the answers

What is an implication of a single-threaded execution model in JavaScript?

It limits concurrency and parallel processing Signup and view all the answers

What is a closure in JavaScript?

A feature that allows functions to access parent scope variables after returning. Signup and view all the answers

What describes the role of the scope chain in closures?

It refers to the order in which variables are accessed in nested functions. Signup and view all the answers

What happens to the variables in a closure when the parent function returns?

They remain accessible to the closure function. Signup and view all the answers

What is the primary purpose of the map method in JavaScript?

To transform each element in the original array and return a new array. Signup and view all the answers

In the reduce method, what does the accumulator represent?

A variable that collects the total during reduction. Signup and view all the answers

Which of the following statements about the filter method is correct?

It returns a new array with elements that pass a specified test condition. Signup and view all the answers

When a function is created, what does it carry with it in terms of its environment?

Variables from its parent function, forming a closure. Signup and view all the answers

Which of the following best describes how closures can be metaphorically understood?

As a backpack that carries along parent scope variables. Signup and view all the answers

What does the reduce method output when operating on an array?

It outputs a single cumulative value. Signup and view all the answers

Which of the following statements is NOT true about closures in JavaScript?

Closures are created manually by developers. Signup and view all the answers

Study Notes

Deconstructing the Monster Definition

JavaScript is a high-level programming language, meaning that it is designed to be easy for humans to read and write.
JavaScript is garbage-collected, which means that memory management is handled automatically, without the developer needing to worry about it.
JavaScript is either interpreted or just-in-time compiled. This means that the code is either executed directly by the browser or compiled into native machine code at runtime.
JavaScript is a multi-paradigm language, meaning that it supports multiple programming styles such as procedural, object-oriented, and functional programming.
JavaScript is prototype-based, which means that objects inherit properties and methods from their prototypes.
JavaScript features first-class functions, meaning that functions are treated like any other data type.
JavaScript is a dynamic language, meaning that data types are not fixed and can change during runtime.
JavaScript is single-threaded, meaning that only one task can be executed at a time. However, JavaScript utilizes a non-blocking event loop which allows the browser to carry out other work such as rendering elements and handling user input without blocking the main thread of execution. This gives the illusion of multi-threading, but it’s not the same.

Working with Arrays

The .push() method adds elements to the end of an array while the .unshift() method adds elements to the beginning of the array.
The .pop() method removes the last element of an array while the .shift() method removes the first element of an array.
The .map() method creates a new array by applying a function to each element of the original array.
The .filter() method creates a new array by filtering the original array with a test condition.
The .reduce() method reduces all elements of the original array to a single value by applying a function.
The .includes() method returns true if the array contains the specified element and false otherwise.
The .every() method checks if all elements of the array pass a specified test condition and returns true if they do, otherwise false.
The .some() method checks if any element of the array passes a specified test condition and returns true if they do, otherwise false.
The .indexOf() method returns the index of the first occurrence of a specified element in the array.
The .slice() method returns a new array that contains a portion of the original array.
The .splice() method modifies the content of the original array by removing or replacing existing elements.
The .concat() method concatenates two or more arrays into a new array.
The .find() method returns the first element of the array that satisfies a specified test condition.
The .join() method combines all array elements into a single string separated by a specified string separator.
The .forEach() method executes a provided function for each element of the array.
The .reverse() method reverses the order of the elements in the array.
The .sort() method sorts the elements of the array in ascending or descending order depending on the sort method.
The .flat() method flattens an array to a certain depth.
The .fill() method replaces all elements in an array with the provided value.
The .flatMap() method applies a function to each element of the array and then flattens the result.

Advanced DOM and Events

The DOM represents a web page as a tree structure of nested nodes.
Each node in the DOM is an object that represents an HTML element, text, or attribute.
The DOM can be accessed by JavaScript to manipulate the content and style of a web page.
Events are user or browser actions that occur on a web page, such as clicks, key presses, and page loads.
Event listeners are used to attach functions that will execute when an event occurs.
Event handlers are functions called when an event takes place.
Events can be used to build interactive web applications.

How The DOM Really Works

The DOM is a representation of the HTML structure of a web page.
The DOM is what JavaScript uses to manipulate the content and style of a web page.
The DOM is dynamically updated whenever the HTML of a web page changes.
The DOM is designed to provide a simple and easy-to-use API for manipulating HTML.

Scope Chain

The scope chain is a hierarchical structure that determines the visibility and accessibility of variables.
The scope chain starts with the local scope then crawls up the chain to global scope searching for the variable.
Variables declared with var are hoisted to the top of the function scope.
Variables declared with let and const are not hoisted.

Closures Summary

A closure is a function that has access to its own scope as well as any variables that were in scope when the closure was created.
Closures are created automatically by JavaScript and cannot be explicitly created.
Closures are useful for creating functions that retain state between calls.
Closures can be used to create private variables.

Data Transformations with `map`, `filter`, and `reduce`

The .map() method iterates over an array and applies a function to each element, returning a new array with the results.
The .filter() method iterates over an array and applies a function to each element, returning a new array with only the elements that pass a specified test.
The .reduce() method iterates over an array, applying a function to each element and an accumulator, eventually returning a single value.

Which Array Method To Use?

When you want to create a new array based on the original array use .map(), .filter(), or .slice().
When you want to modify the original array use methods that mutate the array like: .push(), .pop(), .unshift(), .shift(), .splice(), or .sort().
When you want to find a specific element in the array use .find(), .findIndex(), or .includes().
When you want to transform all array elements into a single value use .reduce().
When you want to loop over an array use .forEach().
When you need to know if all elements in an array meet a given test condition use .every().
When you need to know if at least one element in an array meets a given test condition use .some().
Consider using .flat() to flatten nested arrays.
Use .join() to combine all the elements of an array into one string.
Consider using .fill() to fill an array with a set value.
Use .flatMap() to map and flatten an array simultaneously.

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Description

This quiz covers fundamental concepts of JavaScript, including its high-level nature, memory management, and programming paradigms. Explore how JavaScript's unique features, such as prototype-based inheritance and first-class functions, contribute to its versatility as a programming language.