JavaScript Call Stack Explained!

Hello There 😁. In this Blog Post, I'm going to explain something most javascript developers tend to ignore or don't feel like learning. Today we are going to have a look at the javascript call stack 😃

Now... You might be asking yourself why do I need to know this?

Well... To be honest, even I don't like this topic but it's good to know how things work in the background & also understanding this will help you debug your code easily 😃

let's dive in

What is JavaScript CallStack?

In Simple Words, Javascript call stack is a way for the JavaScript interpreter to manage the invocation of multiple functions

  • It keeps track of what function is currently running and what function is called from within that function
  • When a script calls a function, the interpreter adds it to the call stack and then starts carrying out the function.

    The call stack adds a function on top of other functions and when it's done with that function it removes it from the stack ( last in, first out )

For example:

We have Two functions below

1 function there() {
2 return hello() + " there";
3 }
5 function hello() {
6 return "Hello";
7 }
9 there();
  • We have Two functions Here there() & hello().
  • function there() returns the return value from the functionhello() which in our case is the string "Hello" + the string " there" which combined makes it Hello there

  • On line 9 we are invoking the function there();

  • The JavaScript engine ignores all other functions till it sees the function invocation. In our Case its there()

Lets visualize what's happening in the call stack 😃

call stack pointing.png

  • Here in the chrome debugger, there are many things But, I want you to focus on the call stack section on the right side.

  • As I go one step forward each time the chrome debugger will show us what's really happening.

Lets begin!

  • call stack pointing line 2.png

  • First, we are calling the function there().

  • there() is added to the call stack.

  • We have a return statement on line 2. which returns function hello(). So before we go all in to complete the return statement we have to go into the function hello().

  • call stack pointing line 3.png

  • Here we are on line 6. Because we had the hello() function on line 2, hello() is added to the call stack. You can also see it is added on top of there() because that's how the call stack works. they are added on top of each other because its LAST IN FIRST OUT .

  • call stack pointing line 4.png

  • Now once it is done with the hello() function return statement, the function hello() is removed from the stack and it will go back to line 2 to finish the there() return statement.

  • call stack pointing line 5.png

  • Now that it's done with the function there() it will be removed from the call stack.

If you learned something from this post please do share it with your friends :D & also thank you so much for reading 💜

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Preetika Taneja's photo


Rohil's photo

Thanks, preetika 💜💜

NerdyMuslim's photo

love this

Rohil's photo

Thanks :)