函数作为返回类型javascript

Question

I am trying to create a closure

function init(x){
     var y = 10;
     return function display(a){
        return y + a + x;
     }
     display(5);
}
init(4);

Above closure should return 19. However, it returns a function.

Answer 1

The return is in front of the function, not the call.

function init(x){
     var y = 10;
     function display(a){
        return y + a + x;
     }
     return display(5);
}
init(4);

Answer 2

You have to move the "return". The return keyword will end the code execution of the function and return the value that's passed to the return (in your case a function). If your result has to be 19, consider using the following code:

function init(x) {
     var y = 10;

     function display(a) {
        return y + a + x;
     }

     return display(5);
}

init(4);

Answer 3

The last line in your init function is unreachable , once it's after a return statement. If you want to return a primitive value, you have to return the result of the display function.

function init(x){
     var y = 10;
     function display(a){
        return y + a + x;
     }
     return display(5);
}
init(4);