You Must Know These JavaScript Interview Questions and Answers

Curious about what kind of questions hiring managers ask when looking for a JavaScript developer? Take a look at these commonly asked JavaScript interview questions we’ve researched for you.

As a programming language, JavaScript is highly regarded for its ability to create dynamic and engaging webpages. It has rapidly become one of the most in-demand skills, offering a plethora of job options for beginners and skilled professionals alike. However, due to the intricacy of JavaScript programming, finding qualified JavaScript developers can be a challenging task.

To guarantee that job candidates have the required knowledge of both frontend and backend technologies and the aptitude to efficiently fulfill their responsibilities, recruiters must take essential measures. In addition, to acquire a comprehensive insight into candidates’ capabilities, it’s necessary to formulate a customised set of interview questions.

Explore this series of JavaScript interview questions, ranging from elementary to advanced.

  1. A common JavaScript interview question:

    Enumerate the different types of error names in JavaScript?

    Answer: There are six primary types of Error Name values in JavaScript, which are:
    • Evaluation error:

      This is an error that occurs in the eval() function. (However, newer versions of JavaScript don’t contain it.)
    • Range error:

      This error occurs when a value outside of the defined range is entered.
    • Reference error:

      This error occurs when an undefined variable is used in the code.
    • Syntax error:

      This type of error indicates incorrect code syntax.
    • Type error:

      This type of error occurs when an unknown term is entered.
    • URI error:

      This error occurs when there is an issue with the encodeURI() method.
  2. A fundamental JavaScript interview question:

    Define the key distinctions between a function expression and a function declaration.

    Answer: A function declaration is a standalone statement in the main code that specifies a function along with its respective parameters. On the other hand, a function expression is a function that’s generated within another syntax expression or statement.

    In Strict mode, function declarations placed in a code block are visible throughout the entire block, whereas function expressions are exclusively available within the scope of the code block in which they have been declared.

    Upon execution of the code, a function expression is generated and can be used from that point onwards. However, a function declaration can be executed prior to the actual definition of the function.

    Note: This is a critical question while interviewing for JavaScript, since functions form one of the most essential components of any programming language.
  3. An intermediate level JavaScript interview question:

    What distinguishes attributes from properties?

    Answer: In the DOM renderer, an attribute represents the initial state, while a property indicates the current state.

    JavaScript Document Object Model (DOM) objects in some cases have characteristics that are similar to instance variables. Properties, which can be of various types, can be accessed by invoking the prop() function of jQuery or by interacting directly with the object.

    Attributes are a part of Hypertext Markup Language (HTML) and are dissimilar to the Document Object Model (DOM) since they don’t have the same capabilities. Unlike properties, attributes are made up of string data.
  4. An advanced JavaScript interview question:

    What is the purpose of the call() method?

    Answer: The call() method is an exemplar of the object-oriented characteristics of JavaScript. It specifies the Owner Object.

    In addition, developers can utilise the call() method to leverage another object’s method along with its corresponding arguments. This feature relies on the fundamental principle of JavaScript that identifies a function as a global Object Function if it’s not identified as a method of a JavaScript object.
  5. An advanced JavaScript interview question:

    What is the purpose of the isNaN() function?

    Answer: The isNaN() function serves a singular purpose, which is to verify whether a value is an illegal number.

    The isNaN() function returns a Boolean object with a value of true or false, and it can be used to detect program errors. Moreover, this function can aid in preventing potential runtime errors.
  6. An intermediate level JavaScript interview question:

    What would be the output of “console.log(1 2 3); console.log(3 > 2 > 1);”?

    Answer: Owing to the left-to-right evaluation of expressions in JavaScript, the first statement will be true, but the second statement will return a false output.

    Note: Hiring managers may use this JavaScript interview question to evaluate an applicant’s comprehension of how code is executed in JS.
  7. An advanced JavaScript interview question:

    What is the significance of the ‘this’ keyword?

    Answer: The ‘this’ keyword is utilized to refer to JavaScript objects. Within the class declaration, it makes reference to the present JS objects.
  8. An intermediate level JavaScript interview question:

    Could you elaborate on the various techniques utilized for creating an array object in JavaScript?

    Answer: In JavaScript, there exist three techniques for constructing an array.
    • Creating an array instance, e.g. let exArray = new Array();
    • Using an array constructor, such as var exArray = newArray(“hire,””Works,””developers”);
    • Using an array literal, e.g. var exArray = [“hire”,”Works”,”developers”];
  9. An advanced level JavaScript interview question:

    What is meant by NEGATIVE INFINITY in JavaScript?

    Answer: NEGATIVE INFINITY is a static property in JavaScript that arises when dividing a negative number by zero. It possesses the following crucial characteristics:
    • It is not necessary to construct multiple objects to gain access to NEGATIVE INFINITY.
    • The NEGATIVE INFINITY property holds the identical negative value as the global object’s infinity property.
  10. An advanced JavaScript interview question:

    What is the function of a History Object?

    Answer: A History Object in a browser has the capability of navigating between various pages, including moving back and forth between the presently viewed page and another. In JavaScript, three distinct methods exist for using a History Object:
    • Use history.back() to go back to the previous page.
    • Type history.forward() to proceed to the next page.
    • Bring up a customized page using history.go(number).


Keep in mind that the JavaScript interview questions discussed above serve only as a starting point for assessing the knowledge and skills of a potential JavaScript developer. It is highly recommended to ask more than a dozen questions to evaluate the applicant’s proficiency in the area, ensuring they are the right fit for the job role.

If you find yourself stressed out by resumes, technical interviews, coding challenges, and overall recruitment procedures, take a look at Works.

Works offers complete assistance to organisations in fulfilling their staffing needs. With a simple click of a button, Works can help locate skilled JavaScript developers that cater to the organization’s requirements.

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