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JavaScript Fundamentals Questions

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Instructions
For each question, select the best answer from the options provided. You can view detailed explanations immediately after answering. Navigate through pages using the controls below.
Question 1

What will the following code output? console.log(typeof null)

Question 2

What is the output of: console.log([1, 2, 3].map(x => x * 2).filter(x => x > 3).reduce((a, b) => a + b, 0))

Question 3

What does the 'this' keyword refer to inside a regular function declared with 'function' keyword in strict mode?

Question 4

What is a closure in JavaScript?

Question 5

What will this code output? let a = {}; let b = { key: 'b' }; let c = { key: 'c' }; a[b] = 123; a[c] = 456; console.log(a[b]);

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