In a UI with nested dropdown menus, a developer wants to ensure that clicking a nested menu item does not trigger the click event of its parent menu. What method can be used to stop the event from reaching the parent menu?
- event.stopPropagation()
- event.preventDefault()
- event.stopImmediatePropagation()
- event.cancelBubble()
To prevent the event from reaching the parent menu when clicking a nested menu item, you can use the event.stopPropagation() method. This will stop the event from propagating up the DOM tree and prevent the parent menu's click event from being triggered. event.preventDefault() is used to prevent the default behavior of an event, not to stop event propagation.
What is the main difference between function declaration and function expression in JavaScript?
- Function declarations are hoisted, while function expressions are not.
- Function expressions can be named or anonymous, while function declarations must have a name.
- Function declarations are used for defining methods in objects, while function expressions are used for standalone functions.
- Function expressions are more efficient than function declarations.
The primary difference between function declaration and function expression in JavaScript is hoisting. Function declarations are hoisted, which means they are moved to the top of their containing scope during compilation. This allows you to call the function before it's declared in your code. Function expressions, on the other hand, are not hoisted, so they can only be used after their declaration in the code. Understanding this difference is crucial for managing the order of function calls in your JavaScript programs.
What issues might arise due to JavaScript's prototype chain, and how might they be mitigated?
- Issues may include unintentional property overwrites, inefficiency due to long chains, and unexpected inheritance. Mitigation involves using techniques like Object.create(), encapsulation, and avoiding global scope pollution.
- Issues include limited encapsulation, increased memory usage, and reduced performance. Mitigation is achieved through using classes, constructors, and the ES6 "super" keyword for proper inheritance.
- Problems include circular references, inability to hide properties, and difficulties with class-based modeling. Mitigation is achieved by avoiding circular references and using ES6 classes.
- Problems might involve conflicts between prototypes, slow property access, and limited flexibility. Mitigation requires optimizing property access and using mixins.
JavaScript's prototype chain can lead to issues like unintentional property overwrites, inefficiency, and unexpected inheritance. To mitigate these, developers can use techniques like Object.create() to create clean, isolated objects, encapsulation to hide properties, and avoid global scope pollution.
You're debugging a JavaScript application and notice that a function defined within an object method using an arrow function is not behaving as expected. The "this" keyword is not referring to the object. What could be the reason for this?
- Arrow functions always bind "this" to the object
- Arrow functions don't have their own "this"
- Objects cannot contain arrow functions
- The object's properties are incorrectly defined
Arrow functions in JavaScript do not have their own "this" context. Instead, they inherit the "this" value from their containing function or the global context. If an arrow function is used inside an object method, it will use the "this" from the surrounding scope, which might not be the object itself.
When using querySelectorAll, the returned object is a _______.
- NodeList
- HTMLCollection
- Array
- Element
When you use querySelectorAll, it returns a NodeList. A NodeList is a collection of DOM elements that match the specified selector. Unlike an HTMLCollection, a NodeList is not live, which means it won't change dynamically as the document does.
How does JavaScript’s prototype inheritance differ from classical inheritance models?
- JavaScript uses prototype-based inheritance, allowing objects to inherit directly from other objects.
- JavaScript's prototype inheritance is dynamic and allows objects to change their prototype during runtime.
- In classical inheritance, classes define objects, while JavaScript's prototype inheritance relies on objects and their prototypes.
- JavaScript's prototype chain is single, while classical inheritance can involve multiple parent classes.
JavaScript's prototype inheritance is dynamic, which means you can modify an object's prototype at runtime, adding or removing properties and methods. Classical inheritance is typically static, where classes define the structure beforehand. This dynamic nature allows for greater flexibility but can also lead to unexpected behaviors if not managed properly.
You're building a weather application and you're using the Fetch API to request weather data from a third-party API. However, you realize that the application does not properly handle when the API is down. How would you handle this to inform the user?
- Implement a try-catch block to catch network errors and display a user-friendly message.
- Use the finally block to handle any errors and show an alert to the user.
- Utilize the window.onerror event to detect API failures and log them.
- Set up a timer to periodically check the API status and notify the user if it's down.
To handle API failures and inform the user, you should implement a try-catch block around the fetch request. This allows you to catch network errors, like when the API is down, and then display a user-friendly message or take appropriate action. The other options are not recommended for handling API failures effectively.
What is the result of the comparison operator === if the operands are of different types?
- FALSE
- TRUE
- Undefined
- Error
The comparison operator === (strict equality) in JavaScript returns true if the operands are of different types and have the same value. JavaScript performs type coercion with ==, but === strictly checks both value and type.
What is the time complexity of the unshift() method in JavaScript arrays?
- O(n)
- O(1)
- O(log n)
- O(n log n)
The unshift() method in JavaScript arrays has a time complexity of O(n), where "n" represents the number of elements in the array. This is because it needs to shift all existing elements to make room for the new element at the beginning. The higher the number of elements, the longer it takes.
Which design pattern can be used to create a family of related or dependent objects without specifying their concrete classes?
- Factory Method Pattern
- Abstract Factory Pattern
- Singleton Pattern
- Prototype Pattern
The Abstract Factory Pattern allows you to create families of related or dependent objects without specifying their concrete classes. It provides an interface for creating objects in various categories while ensuring their compatibility within the family.