I have seen JS code written using
if(!!a){
//something here
console.log('something');
}
I don't understand what the preference of doing this is compared to:
if(a){
//something else here
console.log('something else here');
}
Do you gain anything by typing !! in the expression with JS?
The if statement checks for the truthiness of the expression passed to it. The !! coerces truthiness into boolean. Therefore doing:
if (!!a) {}
is exactly the same as:
if (a) {}
This smells strongly of cargo-cult programming or influence form another language.
It's about truthy and falsy:
Everything in JavaScript has an inherent Boolean value, generally known as either truthy or falsy.
The following values are always falsy:
- false
- 0
- ""
- null
- undefined
- NaN
All other values are truthy, including "0" (zero in quotes), "false" (false in quotes), empty functions, empty arrays, and empty objects.
In your case, I don't think it is useful, since an if already uses the truthy/falsy value of the condition:
if (0) {
// this will never be executed
}
The !! can be used like this:
return !!myObject.length; // returns true if myObject.length > 0, false otherwise
return myObject.length > 0; deserves to be strung up by their ankles.
!! use case ;) Do you find a better one?Some samples to understand :
var el = document.getElementById('el');
var log = function(val){
// el.innerHTLM+='<div><pre>' + JSON.stringify(val , null , ' ') +'<\pre></div>';
el.innerHTML+='<div><pre>' + val +'<\pre></div>';
};
var a = 'Helo';
log('a = ' + a);
log('! a = ' + ! a);
log(' !! a = ' + !!a );
log('---');
log('true =' + true);
log('!true =' + !true);
log('!!true =' + !!true);
log('---');
log('false =' + false);
log('!false =' + !false);
log('!!false =' + !!false);
log('---');
log('null =' + null);
log('!null =' + !null);
log('!!null =' + !!null);
log('---')
log('undefined =' + undefined);
log('!undefined =' + !undefined);
log('!!undefined =' + !!undefined);
log('0 =' + 0);
log('!0 =' + !0);
log('!!0 =' + !!0);
log('---');
log('1 =' + 1);
log('!1 =' + !1);
log('!!1 =' + !!1);
log('---');
log('[] =' + []);
log('![] =' + ![]);
log('!![] =' + !![]);
log('---');
log('{} =' + {});
log('!{} =' + !{});
log('!!{} =' + !!{});<div id='el'>Use case:</div>
!! does, you haven't actually answered the question "Do you gain anything by typing !! in the expression with JS?" - i.e., is there any point in using it in an if condition?
is there any point in using it yes millions, you can use it now because you saw the beahviour !!! does, but the question was that since everything in JS has an inherent truthy value anyway, is there any point in using it in an if condition (i.e., are there any situations where using it would give a different result in the if condition than not using it). The answer to that is quite simply "no". It's completely redundant in an if condition. To be honest, your answer does sort of show that, but without actually saying it explicitly.
atobool.booleanvalue in theifconditionifalready cast the expression it checks to bool in order to do the checking. So, why the!!?