argument and variable in function problem ?

[espace]

hi,

i really don't understand this !

why when i put an argument on the function in the CASE 1 and call this function with a the variable count_player it doesn't works ?

in the  CASE 2 it works with simply the variable as argument.

Normally the CASE 1 must works, why is not the case ?

 

//CASE 1

var count_player = 0

launch_player=(count) =>{
count++
}

launch_player(count_player) //return 0
launch_player(count_player) // return always 0









////////////////////////////
//CASE 2

var count_player = 0

launch_player=(count_player) =>{
count_player++
}

launch_player(count_player) //return 0
launch_player(count_player) // return 1 ok it works 

 

[BobF]

Your use of an implicit return in an arrow function is invalid in both case 1 and 2. An implicit return in launch_player should look more like this:

launch_player = (count) => count + 1;

You can read more about using implicit returns with arrow functions here.

[mattstyles]

Neither of your cases returns anything as you've used curly braces to define a function body and not returned anything from that function body. I'm not sure why you're saying it's returning anything currently, because it does not.

In any case JS will pass by value for primitive types so if you're trying to increment the global variable it won't work by passing it as an argument to a function without also declaring an assignment to that variable later.

[espace]

hi, thanks

how do you do so to have a pure function ? i don't really understand what you describe to soluce that...

[espace]

in firefox console

function add(a){a=a+1; return a}
add(3) //return 4

it's the same however....

[espace]

finded

 

var count_example=0

function countor(count) {
    return function () {
        return ++count;
    };
}

var count_increment = countor(count_example);

alert(count_increment()); // 1
alert(count_increment()); // 2
alert(count_increment()); // 3

 

[mattstyles]

So that is sometimes referred to as a thunk and its a great pattern using closures to encapsulate data. Effectively you're setting an initial state for your function to use and it then exposes that 'internal' state when invoked.

`function add (i) {return ++i}` is a pure function. If you want it to increment and store a value from elsewhere then you'd have to do an assignment somewhere i.e.

function add (num) {
  return ++num
}

var value = 0
value = add(value)
value = add(value)

console.log(value)
// 2

// Without assignment value never changes
add(value)
add(value)

console.log(value)
// 2

If you want to 'trap' that initial value in there and then only access it when you want to increment it then your solution is perfect by using a closure.