Top 100 JavaScript Interview Questions and Answers 2023

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Undeclared variables are created when you assign a value to an identifier that is not previously created using var, let or const. Undeclared variables will be defined globally, outside of the current scope. In strict mode, a ReferenceError will be thrown when you try to assign to an undeclared variable. Undeclared variables are bad just like how global variables are bad. To check for them, wrap its usage in a try/catch block. Like objects, they can be assigned to variables, passed to other functions, and returned from functions.

senior javascript developer interview questions

Therefore, it is easier to insert rogue code in the document and make the web page unstable. DOM stands for Document Object Model and is responsible for how various objects in a document interact hire javascript programmer with each other. DOM is required for developing web pages, which includes objects like paragraphs, links, etc. These objects can be operated to include actions like add or delete.

Write a function to find the factorial of a given number in JavaScript.

Closures give access to the outer function’s scope from the inner function’s scope. To define a closure, create a function inside another function to expose it. The callback is a typical function of JavaScript that can be passed as an option or argument of JavaScript. Users are given calls to react to different kinds of triggered situations. Local Variables- Local variables have no scope and are used only once in the whole program. As JavaScript is an object-oriented scripting language, it is very easy to create objects in JavaScript.

  • Many of the most popular JavaScript libraries are doing this because it creates a closure around the entire contents of the file.
  • Generator function are executed yield by yield i.e one yield-expression at a time by its iterator where as Async-await, they are executed sequential await by await.
  • If no value has been given to the variable then, it is called a null object null value.
  • Blur function is used to remove the focus from the specified object.
  • Method checks if the queue is empty, the size method returns the number of elements in the queue, and the print method logs the contents of the queue to the console.
  • The outer loop controls how many times the inner loop runs and the inner loop compares each pair of adjacent elements.

As shown here, this becomes more than just a stylistic preference in JavaScript. In the outer function, both this and self refer to myObject and therefore both can properly reference and access foo. You can fix the length according to you of a predefined array to zero. Generator function are executed yield by yield i.e one yield-expression at a time by its iterator where as Async-await, they are executed sequential await by await. One can choose to jump out of a function and let outer code to determine when to jump back into the function.

What is the definition of the prompt box?

With bubbling, the event is first captured and handled by the innermost element and then propagated to outer elements. The execution starts from that event and goes to its parent element. Then the execution passes to its parent element and so on till the body element. Reading a cookie is just as simple as writing one, because the value of the document.cookie object is the cookie. So you can use this string whenever you want to access the cookie. For example, Test and test are two different variables.

The implementation above can also empty arrays, but it is usually not recommended to use this method often. This way of emptying the array will also update all the references to the original array. Strict mode is a way to introduce better error-checking into your code. Since 2 and 5 are integers, they will be added numerically. And since 3 is a string, its concatenation will be done. The ” ” makes all the difference here and represents 3 as a string and not a number.

What are the ways used to read and write a file in JavaScript?

Write a function to implement a binary tree in JavaScript. Write a function to implement bubble sort in JavaScript. Write a function to implement binary search in JavaScript. As an argument and first checks if it is equal to 0 or 1.

In such a case, if the handler of the child is clicked, the handler of the parent will also work as if it were clicked too. Blur function is used to remove the focus from the specified object. Continue statement continues with next statement of the loop.

Q10. Can you assign an anonymous function to a variable and pass it as an argument to another function?

JavaScript is also known as a scripting language for web pages. This function takes a node in a binary tree as an argument and performs a depth-first search, printing out the value of each node visited. It first checks if the current node is null, and if so, it returns. Otherwise, it logs the value of the current node to the console. Then, it recursively calls itself on the left and right child nodes of the current node, if they exist.

senior javascript developer interview questions

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