What is an execution context and call stack?

Definition:

An execution context is the information JavaScript uses while running a piece of code, including its variables, scope and this value. The call stack tracks which function is currently running and where execution should return. Each function call adds a context, and returning removes it.

Key points:

• An execution context holds the information needed to run some code.

• The stack tracks active function calls; the latest call finishes first.

• Deep recursion can overflow the stack; a long loop can block the thread.

• A function's local variables are separate from the local variables of another call.

• The stack handles synchronous execution; waiting network requests do not remain on it as active JavaScript calls.

Example:

function second() { return 2; }
function first() { return second() + 1; }
console.log(first()); // 3

• first calls second, so second completes before execution returns to first.

Interview point:

• Explain stack overflow and event-loop blocking separately: one is excessive nested calls, the other is work holding the thread too long.

=> Stack overflow happens when the call stack becomes full because too many function calls are added to it. This usually happens because of deep or infinite recursion, where a function keeps calling itself without reaching a stopping condition.

=> Event-loop blocking happens when the JavaScript thread is busy doing a long-running or CPU-heavy task. Since JavaScript normally runs application code on a single main thread, other callbacks, requests, timers, and user interactions have to wait until that task finishes.