Answer
Synchronous: Execution blocks until complete.
Asynchronous: Returns immediately, uses callbacks or promises.
Quick Answer
Synchronous APIs block until complete — good for simple scripts, terrible for UI. Asynchronous APIs return immediately and notify via callback/Promise/event when done — essential for anything that takes time (network, file, timers). Web APIs (fetch, setTimeout, DOM events) are always async. Node.js fs.readFileSync vs fs.readFile exemplifies the difference.
S
SugharaIQ Editorial Team
Verified Answer
This answer has been peer-reviewed by industry experts holding senior engineering roles to ensure technical accuracy and relevance for modern interview standards.
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Source: SugharaIQ