excellent test for scope and the way javascript works

demo.js

function getDemo(demo) {
    const test = function() {
        return demo + ' my friend'
    }
    // an anonymous function is assigned to a variable test
    demo = demo + ' how are you'
    // we do some string concatenation 
    // => "hi how are you" 
    return test()
    // we return test() which invokes the function, as javascript goes from inner to outer scope demo within this function is "hello how are you" and it's concatenated with " my friend", this value is returned 
}

console.log(getDemo("hi"))
// function is called