Essential JavaScript Interview Questions

A collection of 25 JavaScript interview questions. The page focuses on language behavior, including object checks, variable scope, this, strict mode, return parsing, NaN, floating-point precision, integer tests, closures, recursion, event loop timing, logical operators, type coercion, object property keys, and DOM traversal.

Reading notes

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• The page lists questions about typeof checks on objects and a possible pitfall with typeof bar === "object".
• It asks about the output of code that assigns var a = b = 3 inside an IIFE.
• It includes a question about this and self in nested functions.
• It asks why a whole JavaScript source file might be wrapped in a function block.
• It asks for the significance and benefits of 'use strict' at the top of a source file.
• It compares two functions where one return statement is followed by a newline before an object literal.
• It asks what NaN is, its type, and how to test for it reliably.
• It includes a question about 0.1 + 0.2 and equality with 0.3.
• It asks for possible ways to write isInteger(x).
• It asks about console logging order with setTimeout delays of 1000 and 0.
• It asks for a short palindrome function.
• It asks for a sum method that works as both sum(2,3) and sum(2)(3).
• It asks about a loop creating buttons with click handlers that reference i.
• It asks about array mutation after reverse() and push().
• It asks about string and number coercion in several console.log expressions.
• It asks how to avoid stack overflow in a recursive list processor while keeping the recursive pattern.
• It asks what a closure is and requests an example.
• It asks about delayed logging in a loop and how closures can help.
• It asks how || and && evaluate and what values they return.
• It asks about false == '0' and false === '0'.
• It asks what happens when objects are used as property keys.
• It includes a recursive factorial-style function call.
• It includes a nested immediately invoked function expression that logs a captured variable.
• It asks about losing this when a method is assigned to another variable.
• It asks for a function that visits a DOM element and all of its descendants and passes each to a callback.