Lexical scope, closures, and the scope chain explained with a short code example each.
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- What is lexical scope in JavaScript?
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Scope determined by where variables and functions are declared in the code. Inner functions can access variables from their enclosing scopes.- Show a simple lexical scope example.
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function outer() { let x = 5; function inner() { console.log(x); } inner(); } inner can access x because it is in outer's lexical scope.- What is a closure?
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A function that remembers and accesses variables from its enclosing scope even after that scope has finished executing.- Show a closure example with a counter.
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function makeCounter() { let count = 0; return function() { count++; return count; }; } const c = makeCounter(); c() returns 1, then 2. The returned function closes over count.- What is the scope chain in JavaScript?
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The mechanism that looks up a variable by searching the current scope, then parent scopes, until reaching global scope.- What happens when you reference a variable not in local scope?
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JavaScript searches parent scopes up the scope chain. If not found anywhere, a ReferenceError is thrown.- What is function scope?
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Variables declared inside a function are only accessible within that function and nested functions inside it. var has function scope.- What is block scope?
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Scope limited to code blocks (curly braces). let and const have block scope. Variables declared in a block are not accessible outside it.- How does var differ from let and const in scope?
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var has function scope, let and const have block scope. var is also hoisted and can be redeclared in the same function scope.- What is global scope in JavaScript?
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The outermost scope accessible from anywhere in the program. Variables declared at the top level without a function or block are global.- What are free variables?
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Variables referenced in a function but declared in an outer scope. Free variables are what make closures possible.- Show an example of free variables.
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function outer() { let x = 10; function inner() { return x + 5; } } In inner, x is a free variable because it is declared in outer, not inner.- What is variable shadowing?
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Declaring a variable in an inner scope with the same name as a variable in an outer scope, which hides the outer variable.- Show a variable shadowing example.
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let x = 1; function f() { let x = 2; console.log(x); } f() logs 2, not 1. The inner x shadows the outer x.- What is hoisting in JavaScript?
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Variable and function declarations are moved to the top of their scope during compilation. Initializations remain in place.
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