Javascript-尝试将函数分配给变量

Question

I'm just writing a very simple function in javascript to calculate a factorial. I understand that in javascript you can assign a function to a variable.

So I have tried this on an online compiler ( https://repl.it/languages/javascript ) and this is what my code looks like

var mynum = prompt("Enter a number", "<enter a number>");
var answer;
if (isNaN(mynum)){
 console.log(mynum +" is not a number");
}
else{
 console.log("You entered "+mynum);
 answer = function (mynum){
            var i = mynum-1;
            var temp = mynum;
            while(i>0){
              temp = temp*i;
              i--;
            }
            return temp;
  };
 console.log("the factorial of "+mynum+" is "+answer);
}

But when I run this the output keeps including the whole function as "answer"

You entered 23
the factorial of 23 is function (mynum) {var _loopStart = Date.now(),_loopIt =     0;
var i = mynum - 1;
var temp = mynum;setTimeout(function () {_loopStart = Infinity;});
while (i > 0) {if (++_loopIt > 5000 && Date.now() - _loopStart > 150) throw new RangeError("Potential infinite loop. You can disable this from settings.");
  temp = temp * i;
  i--;
}
return temp;

}

However i don't have this issue when i create the function and then call it separately (something like answer = function(mynum).

Can anyone please let me know why this is happening?

Thanks!

Answer 1

Assigning a function to a variable is different from assigning its evaluation.

In your case, you have two solutions available :

Make an effective call to your assigned function at logging time:

console.log("the factorial of "+mynum+" is "+answer(mynum));

Make an effective call to your assigned function at assignation time:

answer = (function (mynum){
  var i = mynum-1;
  var temp = mynum;
  while(i > 0) {
    temp = temp*i;
    i--;
  }
  return temp;
}(mynum));

Both solutions are quite equivalent for your specific situation.

Why?

Because declaring a function like so:

var func = function () {
  console.log("Hello!");
};

Or like so:

function func () {
  console.log("Hello!");
};

Has little difference

Answer 2

As pointed out, you have to call it as a function.

var mynum = prompt("Enter a number", "<enter a number>");
var answer;
if (isNaN(mynum)){
 console.log(mynum +" is not a number");
}
else{
 console.log("You entered "+mynum);
 answer = function (mynum){
            var i = mynum-1;
            var temp = mynum;
            while(i>0){
              temp = temp*i;
              i--;
            }
            return temp;
  };
 console.log("the factorial of "+mynum+" is "+answer (mynum));
}

Alternatively, you could use IIEF(mmediately invoked function expression):

var mynum = prompt("Enter a number", "<enter a number>");
var answer;
if (isNaN(mynum)){
 console.log(mynum +" is not a number");
}
else{
 console.log("You entered "+mynum);
 answer = (function (mynum){
            var i = mynum-1;
            var temp = mynum;
            while(i>0){
              temp = temp*i;
              i--;
            }
            return temp;
  })(mynum);
 console.log("the factorial of "+mynum+" is "+answer);
}

Note that I've added a parenthesis around your function and passed in arguments. That's how you can immediately invoke functions.

Answer 3

When you return a function in javascript such as answer() . You must call it as such.

console.log("the factorial of "+mynum+" is "+answer(mynum));

Answer 4

You need to use the function that you wrote by calling it ie

function add (a,b) {
  return a + b;
}

add(1,2);