You've encountered a do-while loop in a codebase which seems to execute one unnecessary iteration. What might be a possible reason for using do-while in this instance, and what could be an alternative solution?
- The loop is used for input validation.
- The loop is intended to run until a specific condition is met.
- The loop is used for counting items in an array.
- The loop is intended for asynchronous operations.
A common use of do-while loops is for input validation, ensuring that a specific task is performed at least once before checking the condition. The unnecessary iteration might occur because the loop is designed to prompt the user for input before evaluating the condition. An alternative solution could be to use a while loop with the condition checked before the loop, but it wouldn't guarantee at least one execution.
Imagine you're reading a book about the history of web development. The chapter on JavaScript mentions a language that was developed almost simultaneously and competed with JavaScript in the early days. What is the name of this language?
- LiveScript
- CoffeeScript
- TypeScript
- ActionScript
In the early days of web development, there was another language called "LiveScript" that was developed almost simultaneously with JavaScript. Although they had similar names, they were different languages. Eventually, LiveScript was renamed to JavaScript.
The mechanism that allows you to use the structure of a class and alter it for use in another class is known as _________.
- Inheritance
- Polymorphism
- Encapsulation
- Abstraction
The mechanism that allows you to use the structure of a class and alter it for use in another class is known as "Inheritance." Inheritance in JavaScript is achieved through the prototype chain, where a child class can inherit properties and methods from a parent class, allowing for code reuse and extension.
The querySelector method uses _______ selectors to select elements.
- CSS
- XPath
- JSON
- HTML
The querySelector method uses CSS selectors to select elements in the DOM. You can use CSS selector syntax to specify the elements you want to select, making it a powerful tool for finding and manipulating DOM elements based on their attributes and structure.
Which of the following is NOT a primitive data type in JavaScript?
- Object
- Number
- String
- Function
In JavaScript, primitive data types include Number, String, Boolean, Null, Undefined, and Symbol. Object is not a primitive data type; it is a reference data type that can hold collections of key-value pairs or functions. Primitive data types are immutable, whereas objects are mutable.
How does the pop() method behave when applied on an empty array?
- It returns undefined and does nothing
- It throws an error
- It removes the last undefined element and returns it
- It returns null
When the pop() method is applied to an empty array in JavaScript, it returns undefined and does nothing to the array. There are no elements to remove, so it simply returns undefined without causing any errors.
Which method is used to convert a JSON response to a JavaScript object?
- parseJSON()
- toJSON()
- JSON.parse()
- stringifyJSON()
The correct method to convert a JSON response to a JavaScript object is JSON.parse(). JSON.parse() parses a JSON-formatted string and turns it into a JavaScript object. It's commonly used when dealing with data received from APIs or when working with JSON data in JavaScript applications.
Which object is heavily used in AJAX to interact with server-side data?
- XMLHttpRequest
- JSON
- DOM
- Console
XMLHttpRequest is a crucial object used in AJAX (Asynchronous JavaScript and XML) to make HTTP requests to the server and interact with server-side data without requiring a page reload. It allows for asynchronous communication with the server, making web applications more dynamic and responsive.
What is the impact on performance when using a while loop with a condition that evaluates an expression involving function calls?
- High performance impact
- Moderate performance impact
- Low performance impact
- No performance impact
Using a while loop with a condition that involves function calls can have a moderate performance impact. This is because the function calls are evaluated in each iteration, potentially incurring additional processing overhead. It's important to optimize such code to minimize performance issues.
Considering JavaScript's type coercion, what will be the result of [] == ![]?
- TRUE
- FALSE
- undefined
- Throws an error
JavaScript performs type coercion when comparing values. In this case, the empty array [] is truthy, and ![] evaluates to false. When comparing, the empty array is coerced to false, resulting in true. This behavior can be surprising and is a common gotcha in JavaScript.