What is the most common scope chain interview bug?
var shadowing plus hoisting. An inner var with the same name as an outer variable is hoisted with undefined, so a read before the assignment line sees undefined instead of the outer value.
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More FAQs in Scope Chain Interview Questions in JavaScript
Identify where each function was written (lexical scope), walk the scope chain from the current scope up to global, account for hoisting and shadowing, and remember that the chain does not change based on where the function is called.
Because JavaScript is lexically scoped. The scope chain is determined by where the function was written, not where it is called. The caller's variables are not in the function's scope chain.
Closures keep the scope chain alive after the outer function returns. The inner function can still access the outer variables. This is why makeCounter returns a function that keeps incrementing.
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