19. Not ... true!

Reeborg is upset. It’s not raining; it’s not snowing. Yet, he cannot go outside and practise for his hurdles race.

Why, do you ask? It’s because Reeborg is waiting for you to learn about Javascript “not”.

19.1. Time to be negative.

Some programming language, like Python, indicate that something is not true by writing not True which, in Python, is synonymous of False. Javascript, like quite a few other languages, uses a convention where negation is represented by a symbol !

The exclamation mark indicates negation in Javascript. However, instead of appearing at the end of something, like a sentence, it has to appear before something, like some statement that would be normally either true or false. Thus !true is the same thing as false, and !false is the same thing as true.

19.2. Please, make Reeborg happy

You have already written a program that enables Reeborg to jump hurdles; parts of it went something like this:

function run_jump_or_finish () {
    if ( at_goal() ){
        // something
    } else if ( front_is_clear() ){
        // something
    } else {
        // something
    }
}

Try it!

Make Reeborg happy by re-writing this program in three other versions, by choosing different combinations of the negation symbol ! and different combinations of if/else.

You should use the three code samples below but pay close attention to where the negation symbol occur and to what is actually included in each code block.:

// first choice:

function run_jump_or_finish () {
    if ( at_goal() ){
        // something
    } else if ( !front_is_clear() ){
        // something
    } else {
        // something
    }
}

// second choice ... trickier

function run_jump_or_finish () {
    if ( !at_goal() ){
        if ( front_is_clear() ){
            // something
        } else {
            // something
        }
    } else {
        // something
    }
}

// third choice:

function run_jump_or_finish () {
    if ( !at_goal() ){
        if ( !front_is_clear() ){
            // something
        } else {
            // something
        }
    } else {
        // something
    }
}