Execution context and execution stack

The javascript code need to be executed in a specific environnement to work and this environnement is called execution context. An execution context in javascript is like a box, container or everything that you want which stores variables and in which a piece of our code is evaluated and executed

The global execution context

Okay so create a new .js file and added some javascript code, you opened your browser and ran your js code and you saw results so what happen ?

Well like we said javascript is executed in an environnement (execution context), by default all js code outside a function is define in the global execution context, we can also see execution context like an object because in javascript everything is an object in the browser the global execution context correspond to the window object.

Example

let a  = 'lucas';

function first() {
    let b = 'hello';
    second();
    let c = b + a;
}

function second() {
    let d = 'Hi !';
    third();
    let e = d + a;
}

function third() {
    let f = 'Hey !';
    let g = f + a;
}

first();
...

Let's see how this work:

1. First we create and add in the global execution context an a variable which is store into this context.
2. We create three functions first, second, third and we stores them in the global execution context.
3. Still in the global execution context we call the first function, what happen now it's we don't continue to read the code below the call of the first function, but we go back into this function and add on top of the execution stack (list of execution context) the first execution context where first is the name of function, which mean that we now execute the code inside this function.
4. A b variable is created so we store her and we call the second function, now we create a new execution context which is the second execution context the code executed will be now in the second function, we store the d variable and call the third function.
5. A new execution context is created which is the third execution context so we execute the code inside the third function, we store the variables f and d.
6. The third execution context is done and return nothing because the third function is done, from now we removed the third execution context and we're now back in the last execution context which is second execution context.
7. Back in the second execution context we store the e variable and removed the second execution context, we're now in the last execution context which is the first execution context.
8. Then in the first execution context we store the c variable and removed the first execution context and we're back in the last execution context which is global execution context.
9. Finally all execution context are done the result of the first function is display and we can execute the code in the global execution context.

Current errors

This is a list of the main errors that you can meet when you use execution context:

Note: I'm not a wizard there is maybe some issue that you notice above so fell free to open an issue in the github repo if you find a new error not mentioned above.