JavaScript Testing And Optimization (original) (raw)

What is the primary purpose of Jest in JavaScript?

• Unit testing JavaScript code

What does the following code in Jest do?

JavaScript `

const mockFn = jest.fn(); mockFn('test'); console.log(mockFn.mock.calls[0][0]);

`

• Returns the number of function calls
• Logs all arguments passed to the mock function
• Logs the first argument of the first call

What is the purpose of JavaScript's garbage collector?

• Frees memory of unused variables
• Automatically removes unreferenced objects to free memory

What is the most common algorithm used in JavaScript garbage collection?

What is lazy loading in web development?

• Preloading all resources at once
• Caching resources for later use
• Loading resources in parallel
• Delaying the loading of resources until needed

Which attribute enables lazy loading of images in HTML?

What is the main purpose of debouncing in JavaScript?

• To limit function calls to a fixed rate
• To delay a function call until a pause in events
• To cache function results

What is throttling in JavaScript?

• Combining multiple function calls into one
• Delaying function calls until events stop
• Ensuring a function is called at most once in a specified time period

What is the key difference between debouncing and throttling?

• Throttling is faster than debouncing.
• Debouncing is used for lazy loading, while throttling is for memory management.
• Debouncing waits for a pause in events, while throttling ensures periodic execution.
• Both are identical and interchangeable.

What does the following Jest test case do?

JavaScript `

test('adds 1 + 2 to equal 3', () => { expect(1 + 2).toBe(3); });

`

• Logs the result of the addition
• Throws an error if the result is not 3
• Mocks the addition function
• Asserts that the sum of 1 and 2 equals 3

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