index.md

---
title: Call stack
slug: Glossary/Call_stack
page-type: glossary-definition
---

{{GlossarySidebar}}

A **call stack** is a mechanism for an interpreter (like the JavaScript interpreter in a web browser) to keep track of its place in a script that calls multiple {{glossary("function","functions")}} — what function is currently being run and what functions are called from within that function, etc.

- When a script calls a function, the interpreter adds it to the call stack and then starts carrying out the function.
- Any functions that are called by that function are added to the call stack further up, and run where their calls are reached.
- When the current function is finished, the interpreter takes it off the stack and resumes execution where it left off in the last code listing.
- If the stack takes up more space than it was assigned, a "stack overflow" error is thrown.

## Example

```js
function greeting() {
  // [1] Some code here
  sayHi();
  // [2] Some code here
}
function sayHi() {
  return "Hi!";
}

// Invoke the `greeting` function
greeting();

// [3] Some code here
```

The call stack will be empty at the very beginning, and the code above would be executed like this:

1. Ignore all functions, until it reaches the `greeting()` function invocation.
2. Add the `greeting()` function to the call stack list, and we have:

   ```plain
   - greeting
   ```

3. Execute all lines of code inside the `greeting()` function.
4. Get to the `sayHi()` function invocation.
5. Add the `sayHi()` function to the call stack list, like:

   ```plain
   - sayHi
   - greeting
   ```

6. Execute all lines of code inside the `sayHi()` function, until reaches its end.
7. Return execution to the line that invoked `sayHi()` and continue executing the rest of the `greeting()` function.
8. Delete the `sayHi()` function from our call stack list. Now the call stack looks like:

   ```plain
   - greeting
   ```

9. When everything inside the `greeting()` function has been executed, return to its invoking line to continue executing the rest of the JS code.
10. Delete the `greeting()` function from the call stack list. Once again, the call stack become empty.

In summary, then, we start with an empty Call Stack. Whenever we invoke a function, it is automatically added to the Call Stack. Once the function has executed all of its code, it is automatically removed from the Call Stack. Ultimately, the Stack is empty again.

## See also

- [Call stack](https://en.wikipedia.org/wiki/Call_stack) on Wikipedia
- Related glossary terms:
  - {{Glossary("Function")}}