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Understanding the JavaScript Call Stack

What is a ‘call’?

The call stack is primarily used for function invocation (call). Since the call stack is single, function(s) execution, is done, one at a time, from top to bottom. It means the call stack is synchronous.

How many ‘calls’ can happen at once?

    1. When secondFunction() gets executed, an empty stack frame is created. It is the main (anonymous) entry point of the program.
    1. secondFunction() then calls firstFunction()which is pushed into the stack.
    1. firstFunction() returns and prints “Hello from firstFunction” to the console.
    1. firstFunction() is pop off the stack.
    1. The execution order then move to secondFunction().
    1. secondFunction() returns and print “The end from secondFunction” to the console.
    1. secondFunction() is pop off the stack, clearing the memory.

What does LIFO mean?

The last function that gets pushed into the stack is the first to be pop out, when the function returns.

Draw an example of a call stack and the functions that would need to be invoked to generate that call stack.

Call stack example

What causes a Stack Overflow?

A stack overflow occurs when there is a recursive function (a function that calls itself) without an exit point. The browser (hosting environment) has a maximum stack call that it can accomodate before throwing a stack error.

JavaScript error messages

What is a ‘refrence error’?

This is as simple as when you try to use a variable that is not yet declared you get this type os errors.

console.log(foo) // Uncaught ReferenceError: foo is not defined

This is also a common thing when using const and let, they are hoisted like var and function but there is a time between the hoisting and being declared so when you try to access them a reference error occurs, the fact that this happens to let and const is called Temporal Dead Zone (TDZ).

foo = 'Hello' // Uncaught ReferenceError: foo is not defined

let foo

What is a ‘syntax error’?

Some syntax errors like sending a trailing comma when calling a function are handled without error by most recent browsers, but older ones you have to be careful.

What is a ‘range error’?

Try to manipulate an object with some kind of length and give it an invalid length and this kind of errors will show up.

var foo= []

foo.length = foo.length -1 // Uncaught RangeError: Invalid array length

What is a ‘type error’?

This types of errors show up when the types (number, string and so on) you are trying to use or access are incompatible, like accessing a property in an undefined type of variable.

What is a breakpoint?

The breakpoint can also be achieved by putting a debugger statement in your code in the line you want to break.

What does the word ‘debugger’ do in your code?

I’ve added a debugger statement and when running the code above you can see the “history” before reaching that breakpoint.