What is "Promise chaining" in JavaScript?
- A method for nesting multiple if statements
- A technique for connecting multiple Promises
- A way to synchronize asynchronous functions
- A method to define variables
"Promise chaining" is a technique in JavaScript where you can connect multiple Promises together. It allows you to execute asynchronous operations sequentially, making code more readable and manageable, especially when dealing with multiple async tasks.
How does the prototype property behave in arrow functions?
- Arrow functions have a prototype property.
- Arrow functions do not have a prototype.
- Arrow functions inherit their prototype.
- Arrow functions override their prototype.
Arrow functions do not have their own this context and do not have a prototype property. Unlike regular functions, arrow functions do not bind their own this value or have a prototype property. This is a key difference to keep in mind when choosing between regular functions and arrow functions in JavaScript.
Consider a situation where you have a switch statement inside a function, and forgetting to include a break statement leads to a bug. How might this bug manifest in the function’s behavior?
- The function might return the value associated with the first matching case, and all subsequent code within the switch block will execute as well.
- The function will throw an error, indicating a missing "break" statement, and won't execute any code within the switch block.
- The function will automatically insert "break" statements at the end of each case, ensuring correct behavior.
- The function will ignore the switch statement and continue executing the code outside of the switch block.
If you forget to include a "break" statement in a switch case, it will lead to a bug where the function may not behave as expected. Instead of stopping after the first matching case, the switch statement will "fall through" to subsequent cases, causing unintended behavior. The correct option is to use a "break" statement to exit the switch block after handling a case. JavaScript doesn't automatically insert "break" statements, and it doesn't throw an error for missing "break" statements.
The method myArray.find(callback) returns _______ if no element passes the test.
- NaN
- undefined
- an empty array
- -1
The myArray.find(callback) method returns undefined if no element in the array passes the test provided by the callback function. This is because it signifies that no element satisfies the condition. If an element is found that passes the test, it returns that element.
What will happen if the break statement is omitted in a switch case?
- The program will continue to execute the following case(s) until a break or the end of the switch.
- It will skip the current case and move on to the default case.
- It will throw a syntax error.
- It will automatically add a break statement, preventing fall-through.
If you omit the break statement in a switch case, JavaScript will execute the code for that case and continue to execute the code for the following case(s) until it encounters a break statement or reaches the end of the switch statement. This behavior is known as "fall-through."
The keyword ______ is used to specify a block of code to be executed, if the same block that it is directly proceeding does not get executed.
- break
- continue
- return
- finally
The keyword finally is used to specify a block of code that will be executed regardless of whether an exception is thrown or not in a try...catch block. It ensures that cleanup code is always executed.
You are working on a web application where you need to fetch data from an API, perform operations on it, and then use it to update the UI. Which JavaScript feature allows you to handle these asynchronous operations more readably and reliably?
- Callback Functions
- Promises
- Event Loop
- Callback Hell
Promises in JavaScript allow you to handle asynchronous operations more readably and reliably. Promises provide a structured way to work with asynchronous code, making it easier to manage tasks like fetching data from an API, performing operations, and updating the UI when the data is ready.
Which keyword is used to declare a variable with block scope?
- let
- var
- const
- block
The let keyword is used to declare a variable with block scope in JavaScript. Variables declared with let are limited to the block or scope in which they are defined, which is typically within a pair of curly braces {}.
What will happen if the condition in a while loop is always true?
- The code block will never execute
- The code block will execute once
- An infinite loop will occur
- An error will be thrown
If the condition in a while loop is always true, an infinite loop will occur. The code block will keep executing repeatedly, and the loop will never exit. This can lead to the program becoming unresponsive, and it's essential to ensure that the condition in a while loop eventually becomes false to prevent infinite loops.
What is the impact on performance when using a switch statement versus multiple if-else statements for numerous conditions?
- Switch statements are generally faster than multiple if-else statements for numerous conditions because they use direct lookup tables.
- Switch statements are slower than multiple if-else statements for numerous conditions due to increased code complexity.
- There is no significant difference in performance between switch and if-else statements for numerous conditions.
- Switch statements are slower due to the need for explicit type conversions.
Using a switch statement is often more performant when dealing with numerous conditions because it uses direct lookup tables, making it faster and more efficient than a series of if-else statements, which involve sequential comparisons.