return语句显然不返回任何内容

Question

The return statement below doesn't output anything or errors, any reason why?

I tried Chrome and Firefox and repl.it.

Here is the code I have:

//Create a function that uses a return statement
    function multiply(num1, num2){
     return num1 * num2;
    }
    //Call the function
    multiply(10,20 );

I don't get any output or errors.

Answer 1

if you return something, it means it returns something. Right now, you only call multiply(), this function returns a value but you assign it to nothing.

If you use the following:

var returnValue = multiply(5, 10)

your returnValue variable contains the return value of the multiply function.

Answer 2

You don't get any output because you haven't done anything to generate output. You aren't getting any errors because there are no errors in your code. (It's okay to not use the return value of the function; in fact, it's quite common.)

Just returning a value from a function doesn't output it anywhere, it just returns it from the function so you can use it in the code that called the function. One thing you might do with it is output it, but you also might just use it for something else, like including it in a calculation:

 function multiply(num1, num2){ return num1 * num2; } // Using the return value to output it: console.log(multiply(2, 3)); // Using it in another calcuation... const x = multiply(2, 3) + 4; // ...the result of which we might output if we like: console.log(x); 

But again, you might never output the result of a function. For instance, this code uses the result of the function document.getElementById to set up an event handler. Doing that has no output at all:

 let clickCounter = 0; document.getElementById("btn").addEventListener("click", function() { ++clickCounter; }); 

 <input type="button" value="Click Me" id="btn"> 

Answer 3

Unless you're not showing us all of your code, it's because you are not returning the value to anything. Functions that return a value need to have that value used somehow in order for it to be visible. Some examples might be:

1. Using it as a parameter in another method call (eg, logging it to the console):

console.log(multiply(10,20));

2. Setting it to a variable:

var result = multiply(10,20);

3. Using it as a value in another piece of logic:

document.getElementById("equation").textContent = "10 x 20 = " + multiply(10,20);

Without actively capturing and/or using the return value of a method, it will not be displayed anywhere.