You Must Know These JavaScript Interview Questions and Answers

What are some common JavaScript interview questions that hiring managers ask prospective JavaScript developer candidates? Let us investigate.

JavaScript is a widely-recognised programming language that enables businesses to create interactive webpages. It is now one of the most sought-after skills, providing a wealth of job opportunities for both newcomers and experienced professionals. Nevertheless, due to the complexity of JavaScript programming, it can be quite a challenge to locate qualified JavaScript developers.

Recruiters must take the necessary steps to ensure that applicants possess the appropriate familiarity with frontend and backend technologies, as well as the required skills to effectively complete the given tasks. To gain a complete understanding of the prospects’ capabilities, recruiters must also develop a unique set of interview questions.

Here is a collection of JavaScript interview questions ranging from basic to sophisticated.

  1. A fundamental JavaScript interview question:

    Describe the many forms of error name values in JavaScript.

    Answer: There are six main kinds of Error Name values. These are their names:
    • Eval Error: This is an error in the eval() function. (New JavaScript versions do not include it.)
    • Range Error: This error occurs when a number that is outside of the specified range is entered.
    • Reference Error: When an undeclared variable is utilised, this error occurs.
    • Syntax Error: It signifies improper code syntax.
    • Type Error: This occurs when an unfamiliar term is entered.
    • URI Error: This indicates a problem with the encodeURI() method.
  2. A fundamental JavaScript interview question:

    Distinguish between a function expression and a function declaration.

    Answer: A function declaration is a distinct statement within the main body of code that identifies a function and its associated parameters. In contrast, a function expression is a function that is created within another syntax statement or expression.

    Function declarations within a code block are visible throughout the entire block in Strict mode; however, this is not the case with function expressions. Function expressions are only visible within the scope of the code block in which they have been declared.

    When the code is executed, a function expression is generated and can only be used from that point onwards. In contrast, a function declaration can be invoked prior to the definition of the function.

    Note This is a vital JavaScript interview question since functions are one of the most crucial components of any programming language.
  3. A JavaScript interview question for intermediates:

    What is the difference between attributes and properties?

    Answer: In the DOM renderer, an attribute is the original state, and a property is the current state.

    In some cases, JavaScript Document Object Model (DOM) objects have characteristics similar to instance variables. Properties, which may comprise various types of data, can be retrieved by utilising the prop() function of jQuery or by directly interacting with the object.

    Attributes are included in Hypertext Markup Language (HTML) and are distinct from the Document Object Model (DOM), as they do not have the same capabilities. Unlike properties, attributes are composed of string data.
  4. A JavaScript interview question for advanced candidates:

    What exactly is the call() method?

    Answer: The call() function exemplifies JavaScript’s object-oriented characteristics. It indicates the Owner Object.

    Additionally, the call() function facilitates developers in utilising the method of another object, as well as any arguments associated with it. This feature is founded on the JavaScript principle that a function is classified as a global Object Function if it is not considered a method of a JavaScript object.
  5. A JavaScript interview question for advanced candidates:

    What exactly is the isNaN() function?

    Answer: The isNaN() method has just one purpose: to determine whether or not a value is an unlawful number.

    The isNaN() method returns a Boolean object with the value of true or false, which can be used to detect errors in the program. Additionally, this function can be used to prevent potential runtime errors from occurring.
  6. A JavaScript interview question for intermediates:

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

    Answer: Due to the left-to-right evaluation of expressions in JavaScript, the first statement evaluates to be true, whereas the second statement produces a false result.

    Note: Recruiters may use this JavaScript interview question to see whether the applicant understands how code executes in JS.
  7. A JavaScript interview question for advanced candidates:

    What is the purpose of the ‘this’ keyword?

    Answer: The ‘this’ keyword is used to refer to JavaScript objects. Within the class declaration, it refers to the current JS objects.
  8. A JavaScript interview question for intermediates:

    Explain the different methods for creating an array object in JavaScript.

    Answer: In JavaScript, there are three methods for creating an array.
    • Create an array instance
      For example, let exArray = new Array();
    • Make use of an array constructor.
      For example, var exArray = newArray(“hire,””Works,””developers”);
    • Make use of an array literal.
      For instance, var exArray = [“hire”,”Works”,”developers”];
  9. A JavaScript interview question for advanced candidates:

    In JavaScript, explain NEGATIVE INFINITY.

    Answer: Negative Infinity is a static property of JavaScript that is obtained when a negative number is divided by zero. It has the following key features:
    • It is not essential to build several objects in order to have access to NEGATIVE INFINITY
    • The NEGATIVE INFINITY property has the same negative value as the global object’s infinity property.
  10. A JavaScript interview question for advanced candidates:

    What is the purpose of a historical object?

    Answer A browser’s History Object is capable of navigating between different pages, such as moving forward and back from the currently viewed page or from another page. In JavaScript, there are three distinct methods for utilising a History Object which are the following:
    • To return to the previous page, use history.back ().
    • To go to the next page, type history.forward ().
    • To bring up a custom page – history.go(number).


It is important to remember that these JavaScript interview questions are just the starting point for assessing a potential JavaScript developer’s knowledge and skill. Asking more than a dozen questions is highly recommended in order to evaluate the applicant’s expertise in the field. Doing so will ensure that the individual is a suitable fit for the role.

However, if you’re feeling overwhelmed by resumes, technical interviews, coding difficulties, and general recruiting processes, consider Works.

Works offers comprehensive support to organisations in fulfilling their staffing requirements. By simply clicking the mouse, Works can provide assistance in locating experienced JavaScript developers that meet the needs of the organisation.

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