Call stack
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 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 code above would be executed like this:
- Ignore all functions, until it reaches the
greeting()
function invocation. - Add the
greeting()
function to the call stack list.Note: Call stack list: - greeting
- Execute all lines of code inside the
greeting()
function. - Get to the
sayHi()
function invocation. - Add the
sayHi()
function to the call stack list.Note: Call stack list: - sayHi - greeting
- Execute all lines of code inside the
sayHi()
function, until reaches its end. - Return execution to the line that invoked
sayHi()
and continue executing the rest of thegreeting()
function. - Delete the
sayHi()
function from our call stack list.Note: Call stack list: - greeting
- When everything inside the
greeting()
function has been executed, return to its invoking line to continue executing the rest of the JS code. - Delete the
greeting()
function from the call stack list.Note: Call stack list: 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 on Wikipedia
- Glossary