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14 Questions to Ask in a Technical Interview for a Javascript Developer


The purpose of a technical interview is to assess a candidate’s technical skills and knowledge. It is an opportunity for the interviewer to gauge whether the candidate has the necessary skill set to perform the role they have applied for.

When interviewing a candidate for a javascript developer role, there are several key questions that you should ask to get a better understanding of their technical abilities.

In this article, we will share 14 questions that you can ask in a technical interview for a javascript developer role. By asking these questions, you will be able to gain insights into the candidate’s level of expertise and whether they are a good fit for the role.

1. What is a closure in JavaScript?

A closure is a function that encloses its surrounding environment, allowing the execution of the functions defined within it to access the variables, objects, and other data within the environment. Closures in JavaScript allow developers to write code that has a greater degree of complexity while still keeping the code organized and easy to understand. Closures are used to preserve the state and provide encapsulation, inheritance, and more.

2. What is a prototype in JavaScript?

A prototype is an object that has properties and methods that are inherited by other instances of the same object. In JavaScript, every object has an implicit prototype property that determines what objects the object inherits from. This is how inheritance is implemented in JavaScript, where a developer can define how an object should behave and all objects that inherit from that object will exhibit that same behavior.

3. What is the difference between == and === in JavaScript?

The difference between == and === in JavaScript is that the former performs a type conversion when comparing two values, while the latter does not. The == comparison operator performs a type conversion if the types of the two operands are not the same. This means that if the values of the two operands are not the same type, it will try to convert one of the operands to the type of the other before making the comparison. On the other hand, the === comparison operator does not perform any type conversions and will only evaluate to true if the two operands are of the same type and have the same value.

4. What is a ternary operator in JavaScript?

A ternary operator is a conditional operator in JavaScript that is a shorthand way of writing an if-else statement. It has the form ‘condition? expression1: expression2’, where the first expression is evaluated if the condition is true, and the second expression is evaluated if the condition is false. It is a concise way of evaluating a condition and executing a certain code block based on the outcome of the evaluation.

5. What is the use of the isNaN function in JavaScript?

The isNaN function in JavaScript is used to determine if a value is NaN (not a number). This is useful when trying to check if a number has been converted from another type (e.g. from a string) and cannot be accurately interpreted as a number. The isNaN function will return true if the value passed to it is not a number and false if it is.

6. What is the void operator in JavaScript?

The void operator in JavaScript allows you to evaluate an expression to be undefined. It is a unary operator, which means that it takes only one operand. Using this operator will cause the code to evaluate the given expression and then immediately return undefined, without returning any value.

7. What is the use of typeof operator in JavaScript?

The typeof operator in JavaScript is used to get the type of a variable or an expression. It returns a string that describes the variable type or expression it is given, such as number, string, object, etc. This operator is useful when trying to determine the type of a variable or expression in an unknown context.

8. What is this keyword in JavaScript?

The this keyword in JavaScript is an object that refers to the current context. It can refer to different things depending on the context in which it is used, for example, if it is used in a constructor function, it will refer to the object being constructed. This keyword allows developers to access variables and methods from the context in which it is used.

9. Explain the for-in loop in JavaScript.

The for-in loop in JavaScript is a looping construct that can be used to iterate over the properties of an object. The for-in loop checks for all enumerable properties of an object and then executes a block of code for each property. It allows developers to quickly loop through an object and access the properties and values of the object.

10. What is the use of break statement in JavaScript?

The break statement in JavaScript is used to break out of a loop or switch statement. If a break statement is encountered in the loop or switch statement, the loop execution or switch case is immediately terminated and the subsequent statements are executed. This can be used to break out of a loop if a certain condition is met or if an unexpected result occurs.

11. What is the use of continue statement in JavaScript?

The continue statement in JavaScript is used to skip the current iteration of a loop and continue to the next iteration. This can be used if you want to skip a loop iteration if a certain condition is met or if you want to re-evaluate the condition at the start of the next iteration.

12. Explain the use of try-catch block in JavaScript.

The try-catch block in JavaScript is used for exception handling. It is a combination of a try block and a catch block. The try block contains code where exceptions are likely to be thrown, and the catch block is where exceptions that are thrown inside the try block are handled. This block allows developers to handle errors gracefully and avoid errors from causing the program to crash.

13. What is JSON in JavaScript?

JSON (JavaScript Object Notation) is a data-interchange format used to store and exchange data between different systems. It is a lightweight format that is easy to parse and generate. JSON objects are easy to use and can be used to pass data between systems in a standardized format.

14. What is the use of delete operator in JavaScript?

The delete operator in JavaScript is used to delete a property of an object. It takes one parameter, which can either be an object or an array, and deletes the property of the specified object. It can also be used to delete properties from a constructor function, which means that all instances of the object will no longer contain the deleted property.

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