Node.js event loop phases, modules, fs, path, streams, buffers, process, events and npm basics.
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- What is the Node.js event loop?
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The mechanism that allows Node.js to perform non-blocking I/O operations by delegating work to the system kernel and executing callbacks when operations complete.- Name the six main phases of the Node.js event loop.
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timers, pending callbacks, idle/prepare, poll, check, close callbacks- What happens in the timers phase of the event loop?
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Callbacks scheduled by setTimeout() and setInterval() are executed if their delay has expired.- What happens in the pending callbacks phase of the event loop?
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Callbacks deferred to the next iteration of the event loop are executed, typically for I/O operations that failed.- What happens in the idle/prepare phase of the event loop?
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Internal preparation occurs for the next phases; this phase is rarely encountered in user code.- What happens in the poll phase of the event loop?
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The event loop retrieves new I/O events and executes their associated callbacks; it handles file system, network, and other async operations.- What happens in the check phase of the event loop?
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Callbacks scheduled by setImmediate() are executed.- What happens in the close callbacks phase of the event loop?
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Callbacks for closed connections and aborted operations are executed.- What is a Node.js module?
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A reusable block of code whose existence does not accidentally impact other code; a file containing JavaScript functionality that can be used in other files.- What does require() do?
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It loads a module and returns the module's exports so it can be used in the current file.- What is module.exports?
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An object that defines what a module exports and makes it available to other modules that require() it.- What is the difference between CommonJS and ES modules in Node.js?
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CommonJS uses require() and module.exports; ES modules use import and export statements. Node.js uses CommonJS by default unless .mjs extension or type field is specified.- How do you export a function from a module?
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Assign the function to module.exports, for example: module.exports = function() { ... };- What does fs.readFile() do?
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Reads the contents of a file asynchronously without blocking; requires a callback that receives the file data.- What does fs.readFileSync() do?
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Reads the contents of a file synchronously and blocks execution until the read completes; returns the file data directly.
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