closures

I was reading In JavaScript, what is the advantage of !function(){}() over (function () {})()? then it hit me, why use : (function(){})() or !function(){}() instead of just function(){}() ? Is there any specific reason? It depends on where you write this. function(){}() by itself will generate a syntax error as it is evaluated as function declaration and those need names. By using parenthesis or the not operator, you enforce it to be interpreted as function expression , which don't need names. In case where it would be treated as expression anyway, you can omit the parenthesis or the operator.

I think I understand why variables exist outside of the function they were declared in, because you're returning another function: myFunction = function() { var closure = 'closure scope' return function() { return closure; } } A = myFunction(); // myFunction returns a function, not a value B = A(); // A is a function, which when run, returns: console.log(B); // 'closure scope' The way that it's written now, calling A() is like a getter. Q: How can I write myFunction so that calling A(123) is a setter? Try the following: myFunction = function() { var closure = 'closure scope' // value is

In the code below please can someone explain to me why multiple calls to counter result in the value of i increasing each time it is called? My understanding is that as we specifically set i = 0; in makeCounter , each time makeCounter is called through the counter variable, i should be reset to 0. I cannot understand why this is not the case. function makeCounter() { // `i` is only accessible inside `makeCounter`. var i = 0; return function() { console.log( ++i ); }; } // Note that `counter` and `counter2` each have their own scoped `i`. var counter = makeCounter(); counter(); // logs: 1

I have a structure that contains a value and I want to obtain a function that operates on this value: struct Returner { val: i32, } impl<'a> Returner { fn get(&'a self) -> Box<Fn(i32) -> i32> { Box::new(|x| x + self.val) } } This fails compilation: error[E0495]: cannot infer an appropriate lifetime due to conflicting requirements --> src/main.rs:7:18 | 7 | Box::new(|x| x + self.val) | ^^^^^^^^^^^^^^^^ | note: first, the lifetime cannot outlive the lifetime 'a as defined on the impl at 5:1... --> src/main.rs:5:1 | 5 | impl<'a> Returner { | ^^^^^^^^^^^^^^^^^ = note: ...so that the types are