Meaning of !! and how to use it [duplicate]

This question already has an answer here:

• What is the !! (not not) operator in JavaScript? 31 answers
• Double negation (!!) in javascript - what is the purpose? [duplicate] 3 answers

I am writing a code using webstorm IDE, and i wrote an

if statement

in a method like this::

createEvent():boolean {
return this.http.post('/event', { params: {name , location} }).map(res => res.json()).map(res => {
if(event && event.success){
return true;
}
return false;
});
}

Then the IDE suggest i rewrite(simplify) the if statement this way:

createEvent():boolean {
    return this.http.post('/event', { params: {name , location} }).map(res => res.json()).map(res => {
   return !!(event && event.success);
    });
    }

I find it confusing while the system uses a double NOT sign.
Please i need some explanation.