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Javascript Test Questions: Javascript Explained

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Javascript is an incredibly powerful and versatile coding language used in a broad array of web applications. It’s an integral part of many interactive websites, and is even used in game engines and mobile development. To be successful in coding and web development, it’s important to have an understanding of the fundamentals of Javascript. This article will cover all the basics of Javascript, from understanding its syntax to working with objects. By the end, you’ll have the skills to ace any Javascript test questions.

What is Javascript?

Javascript is a lightweight, interpreted coding language found in many web-based applications. It can be used to add dynamic content to pages, control multimedia files, and manage user input for interactive websites. While Javascript started as a web-based language, it has since expanded to include game development, web server programming, and software development.

Javascript is a popular language for web developers, as it is relatively easy to learn and use. It is also a versatile language, as it can be used to create both client-side and server-side applications. Additionally, Javascript is a cross-platform language, meaning it can be used on multiple operating systems and devices. This makes it an ideal choice for developers who need to create applications that can be used on multiple platforms.

Understanding Basic Syntax of Javascript

In Javascript, variables are declared with the ‘var’ keyword. Variables are containers for data and are essential for storing information within a program. Variables can be composed of numbers, strings (e.g. words), and Booleans (true/false).For example..

var myNumber = 10;var myString = ‘hello’;var myBoolean = true;

Another important element of Javascript syntax is the use of operators. Operators are symbols that perform mathematical or logical operations on two or more operands (the values that operators act upon). Popular operators include addition (+), subtraction (-), multiplication (*), division (/), and modulus (%). For example..

3 + 5 = 810 – 2 = 8 4 * 2 = 8 16 / 2 = 8 13 % 5 = 3

Javascript Variables and Data Types

As mentioned earlier, variables play an important role in Javascript programming. It’s important to note that variables in Javascript don’t have a fixed type; they can reference a different type of value at different times. In order to explicitly specify a variable type, you can use ‘const’ or ‘let’ keywords. For example..

const myNumber = 10; //Number let myString = ‘hello’; //String let myBoolean = true; //Boolean

Other data types in Javascript include objects, arrays, dates, regular expressions (patterns of characters used for matching), and functions. Objects are collections of related data often used to store and manage data. Arrays are ordered sets of data, like lists. Dates are used to store and manipulate dates or times. Regular expressions and functions are used for matching patterns or performing complex calculations.

Working with Arrays in Javascript

Arrays are a common data type that can be used to store and work with multiple elements. Arrays can contain elements like strings and numbers, as well as other arrays and objects. To create an array, you use the array constructor with brackets [], such as..

var myArray = [1,2,3]; or var myArray = [‘a’, ‘b’, ‘c’];

In addition to the array constructor, there are several other methods available for manipulating arrays. These include push(), which adds an element at the end of an array, pop(), which removes an element from the end of an array, and sort(), which orders elements of an array from lowest to highest.

Operators in Javascript

Javascript uses several types of operators for manipulating values within a program. Arithmetic operators perform numeric calculations such as addition, subtraction, multiplication, and division. JavaScript also uses comparison or relational operators for comparing values and logical or Boolean operators for determining the truthfulness of a statement. Other operators include assignment and string operators.

Conditional Statements in Javascript

Conditional statements are used to determine whether a certain code block should be executed depending on the result of a given condition. The most common type is the ‘if’ statement, which checks to see if a condition is true. If the condition is true, a code block will be executed; if not, it will not. Other types of conditional statements include ‘switch’ statements which execute code based on various cases, and ‘ternary’ statements which are shorthand versions of ‘if’ statements.

Loops in Javascript

Loops allow code blocks to be executed repeatedly until a certain condition is met. Two of the most commonly used loop types are ‘for’ loops and ‘while’ loops. For loops are used when you know ahead of time how many times a code block should be executed, while while loops keep executing until a certain condition is met. Other loop types include ‘do..while’ loops which will execute at least once before checking its condition.

Functions in Javascript

Functions are blocks of code that allow for reusing code throughout a program without duplicating it. Functions take one or more inputs (parameters) and return a single output (return value). They can also perform various operations on their parameters, such as multiplication or comparison. Functions can make programs more organized and efficient by reducing repetition in code.

Working with Objects in Javascript

Objects are collections of related data that can store key-value pairs. They allow you to organize data into distinct entities and can be accessed using dot notation (objectName.key). JavaScript supports three types of objects: native objects (built-in objects), user-defined objects (created with functions) , and host objects (provided by the browser). It’s important to be familiar with the syntax for each when working with objects.

Constructors and Prototypes in Javascript

Constructors are functions that allow user-defined objects to be created from templates known as classes. Objects created by constructors inherit properties from their prototype object. Prototypes allow additional properties to be added to existing objects without the need for redefining them. It’s important to understand how constructors and prototypes work together in order to create user-defined objects.

Error Handling in Javascript

Error handling allows for catch potential errors before they cause issues in a program. In JavaScript, errors can be handled using the ‘try..catch’ statement which takes care of any exceptions that occur during execution of a program. The ‘try..catch’ statement allows you to catch any errors before they cause issues in your program.

Best Practices for Writing Clean and Readable Code

Writing clean, readable code is essential for ensuring that your program works as expected. This includes things like formatting your code correctly with spacing and indentation, breaking dense code into separate functions or modules, commenting your code where appropriate, and choosing concise variable names. Following these best practices will make debugging your code much easier.

Common Mistakes to Avoid When Writing Code

When writing code it’s important to pay attention to details to ensure that your program works as expected. Common mistakes to watch out for include not handling errors properly, not initializing variables before they are used, writing function that rely heavily on global variables, forgetting to break long code blocks into functions or modules, and using confusing variable or function names.

Tips for Writing Efficient and Secure Code

Writing efficient code is important for ensuring that programs run smoothly without taking up too many system resources or slowing down the user experience. Tips for writing efficient code include reducing redundant calculations, using caching techniques for retrieving data, making use of asynchronous functions or threads where possible, monitoring memory usage closely , and using proper error handling techniques . Additionally, using secure coding practices such as input validation and output sanitization will help prevent malicious code from being injected into your program.

Sarang Sharma

Sarang Sharma

Sarang Sharma is Software Engineer at Bito with a robust background in distributed systems, chatbots, large language models (LLMs), and SaaS technologies. With over six years of experience, Sarang has demonstrated expertise as a lead software engineer and backend engineer, primarily focusing on software infrastructure and design. Before joining Bito, he significantly contributed to Engati, where he played a pivotal role in enhancing and developing advanced software solutions. His career began with foundational experiences as an intern, including a notable project at the Indian Institute of Technology, Delhi, to develop an assistive website for the visually challenged.

Written by developers for developers

This article was handcrafted with by the Bito team.

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