I have the following two codes set. The first alerts 'true', I know that, Its Ok. The second one alerts 'false', I thought that would alert '!function(){return false}'. But, It alerts 'false'. How this second code block alerts false? Could anyone help me understand that please?
var myVar = !function(){return false}();
alert(myVar); //true
var myVar = !function(){return false};
alert(myVar); //false, I dont understand this, how false can come?
First snippet
var myVar = !function(){ return false; }( );
// myVar = false; because invocation ----^
alert(myVar); // !false = true
Second snippet
var myVar = !function(){return false};
// myVar = Function myVar = !(Function) and a Function is *truthy*
alert(myVar); // !true = false
In the first snippet, you're calling it right away, so myVar is false and !false is obviously true.
In the second snippet however, you ain't calling the function. Instead, myVar is now a function, which is truthy. That is, it's considered true. So again !true = false.
Remember, in javascript, false, NaN, null, undefined, 0 , "" are falsey and everything else is truthy.
You should avoid the !function statement. when you use the () at the end of a function, you actually say you want to use the return output of the function. you didn't use it with the last statement.
var myVar = function(){return true}();
alert(myVar); //true
var myVar = function(){return false}();
alert(myVar); //false
This question already has a nice answer from Amit joki
I had read a comment below his answer there the questioner was said that he need more explanation that's why i am posting this answer .
First Case:
var myVar = !function(){ return false; }( );
alert(myVar);
Here myVar is an anonymous function and through the below code it calls itself.
var myVar = !function(){ return false; }( );
That is it, is a self executing anonymous function!
.
a
!function()Using the ! operator before the function causes it to be treated as an expression, so we can call it:
So when we try to alert(myvar);
then it will alert the return value of the myVar function . Already the myVar function return a false and the ! symbol in our code will convert it to true
So it will return true
Think our code is something like below
var myVar = function(){ return 10; }( );
it will also alert true. Because in javascript only false, NaN, null, undefined, 0 , "" are false and other all are truth.
and when the above code changes to
var myVar = !function(){ return 10; }( );
then it will alert false because the statement return 10 is true in javascript and it will converted to false by ! operator
Then in second case :
var myVar = !function(){return true};
alert(myVarz);
Here is no self executing anonymous function. only an anonymous function definition is here. When we try alert(myVar)
myVar is now a function, which is truthy because in javascript only false, NaN, null, undefined, 0 , "" are false and other all are truthy.!!!
And here also ! comes in frond of function like !function(){return true}; soit will convert the true to false.
