What are function statements?

1
The function statement declares a function.
2
A declared function is 'saved for later use', and will be executed later when it is invoked (called).

javascript

Difficulty: 3/10

Topics: hoisting, function declarations, scope and execution context

0-2 years experience

1
We have a legacy file where some helper functions are called at the top of the file, but they are defined at the very bottom. Some of them work fine, but others throw a 'TypeError: undefined is not a function'. What is the difference in how these functions were declared that causes this behavior?
2
Imagine you are writing a utility module. You need to choose between writing 'function calculateTax() {}' and 'const calculateTax = () => {}'. How does your choice affect where in the file you can actually invoke this utility?

2-5 years experience

1
During a code review, a developer wrapped a standard 'function logError()' declaration inside an 'if (process.env.NODE_ENV === "development")' block. Why might this behave unpredictably across different browsers or strict mode settings?
2
We are refactoring a large React codebase from class components to functional components. A teammate wants to convert all helper functions inside the component file to arrow functions assigned to const, while another prefers traditional function declarations. What are the practical implications of this choice regarding hoisting, memory allocation on re-renders, and unit testing?

5-8 years experience

1
When designing a core utility library for a large engineering team, how would you structure your style guide regarding function declarations versus arrow functions? Specifically, how do you balance readability, recursion safety, and the 'temporal dead zone' for junior developers?
2
We're debugging a memory leak in a high-throughput Node.js service. We noticed some functions are declared dynamically inside a hot-path loop. How does the V8 engine optimize function declarations versus dynamically evaluated function expressions, and how would you refactor this to prevent garbage collection spikes?

8+ years experience

1
We are migrating a massive, 10-year-old legacy codebase from ES5 to modern ESNext, and we're seeing bundler tree-shaking issues where unused utility functions aren't being eliminated. How do function declarations versus function expressions impact static analysis and tree-shaking in modern bundlers like Webpack or Rollup, and how would you guide the team to resolve this?
2
Your team is building an extensible plugin architecture where third-party developers inject scripts into our runtime. How do you handle the security and scoping risks associated with global function declarations overriding core APIs, and what sandboxing strategies would you implement at the engine level?

❓How does JavaScript's strict mode alter the scoping of a function declaration inside an if-statement?
❓If a variable declared with var and a function declaration share the exact same identifier, how does the interpreter resolve the conflict during hoisting?
❓Under what circumstances would you deliberately choose a function declaration over an arrow function expression?