Today on Js ( 1 - 31/03/24)

JS Execution context

There are two types of JS execution context

• Global execution context

• Function execution context

• Eval execution context ( won't go in-depth here)

Global Execution context

the global execution context is different for every engine or browser for example, if you go into Chrome and check its GEC you will see a lot of Windows event listeners and such

{} - these curly braces define the GEC

Function Execution context

When a function is called, the JS engine creates an FEC within GEC to execute the code within that function

How does it work? (Overview)

It runs in two phases

• Memory creation phase -> allocation of memory

• Execution phase -> stuff like arithmetic operation is done here

for example :

 let val1 = 10 
 let val2 = 5
 function addNum(num1,num2){
    let total = num1+num2
    return total
 }
 let result1 = addNum(val1,val2)
 let result2 = addNum(5,3)

1-> Global Execution -"this" stores GE 2-> Memory Phase (the steps in which the above is stored ) val1 -> undefined val2 -> undefined addNum -> definition of the function result1 -> undefined result2 -> undefined // This is the first cycle

3-> Execution Phase val1 -> 10 val2 -> 5 // addNum will execute nothing as this is an execution phase so addnum will not do anything // this addNum will make its context box called new executional context which will contain a new variable environment + execution thread every time a function is called a new executional context will be created; when a sandbox(execution context) the memory and execution phase will be repeated So, Memory Phase -> val1 -> undefined val2 -> undefined total -> undefined

Execution context -> processing is done, data manipulating, etc is done num1 -> 10 num2 -> 5 Note: after GE is used it automatically gets deleted as well total -> 15

now it goes back to the previous memory phase and does result = 15 now same stuff with result2 new variable environments and a thread with its two-phase