如何从传递了参数的回调中返回值

Question

I have made a function square (that returns square of the number)and passed it into another function.

var num = 5;
  function square(x){
  return x*x;
}

function display(fn){
  console.log(fn())
}

display(function(){square(num)});

It is not returning me that squared value in display function instead it is returning me 'undefined'.

Answer 1

You don't have to use function(){} to call your function. It is only used to define a function.

Beside this you can just use the fn variable to log to the console, you don't have to use fn()

var num = 5;
function square(x){
    return x*x;
}

function display(fn){
    console.log(fn)
}

display(square(num));

It is also possible to return the value into a variable, if this makes it easier to read for you:

function square(x){
    return x*x;
}

function display(fn){
    console.log(fn)
}

var num = 5;
var calculationResult = square(num);
display(calculationResult);

Answer 2

Here. You just need to return the square(num) inside the display function.

 var num = 5; function square(x){ return x*x; } function display(fn){ console.log(fn()); } display(function(){ return square(num); }); 

Answer 3

You lose the returned value here:

 display(function(){square(num)})

You either have to return it:

 display(function(){ return square(num)})

or you use an arrow function

 display(() => square(num));

or you bind the function:

 display(square.bind(null, num));

Answer 4

display(function(){square(num)});

In your code just write return keyword .

display(function(){return square(num)});

Above code will work fine