Viva Questions

20 short JavaScript viva Q&A.

Common JavaScript Viva Questions and Answers

What is JavaScript? High-level, interpreted scripting language used to make web pages interactive.
Who created JS? Brendan Eich at Netscape, 1995.
Java vs JavaScript? Completely different languages — only the name was a marketing decision in 1995.
Is JS case-sensitive? Yes — Name and name are different.
var vs let vs const? var (function-scoped, hoisted), let (block-scoped), const (block-scoped + immutable binding).
Data types in JS? Primitive: number, string, boolean, null, undefined, symbol, bigint. Reference: object, array, function.
== vs ===? == allows type coercion; === checks both type and value.
What is hoisting? Variable/function declarations are moved to top of scope before execution. var is hoisted but undefined; let/const enter "temporal dead zone".
What is closure? Function that remembers variables from its outer scope even after the outer function returns.
What's an arrow function? Shorter syntax: (a, b) => a + b. Doesn't have its own this.
What is the DOM? Document Object Model — tree representation of the HTML document.
innerHTML vs textContent? innerHTML parses HTML; textContent treats as plain text (safer).
What is a Promise? Object representing eventual completion of an async operation. States: pending / fulfilled / rejected.
What is async/await? Syntactic sugar over Promises — write async code that looks synchronous.
null vs undefined? undefined = variable declared but no value. null = explicit "no value".
What is event bubbling? Event triggered on a child also fires on its ancestors (innermost first).
What is JSON? JavaScript Object Notation — text format for data interchange. JSON.parse() and JSON.stringify().
What is this in JS? Refers to the object that invoked the function (changes based on call context; arrow functions inherit from enclosing scope).
Synchronous vs asynchronous? Sync — line-by-line, blocking. Async — non-blocking (callbacks, Promises, async/await).
What is the event loop? JS runtime mechanism — picks tasks from the queue and executes them on the single-threaded call stack.

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