Functions

函數是設計用於執行特定任務的代碼塊。函數可以幫助組織代碼，避免重複並降低代碼的複雜性。

// Creating the function

    function sum_numbers() {
        var num1 = 5;
        var num2 = 2;
        var sum  = x + y;
        console.log(sum);   
    }

    // The function is only executed after being invoked(被調用):

    sum_numbers(); // The console will show 7

Some important observations about what we've just done:

• We use the  keyword to create a function.
• Then we name the function following the same rules as for naming variables.
• Inside parenthesis we'll add the arguments函數 (or parameters參數) of the function. Even if the function has no arguments, like above, we need to open and close parenthesis when creating and when invoking it.
• Inside the curly braces '{ }' we'll write the block of code we want to be executed every time the function is invoked.
• Semicolons are not needed at the end of function the declarations

Function arguments

By using arguments we can make it dynamic動態的 and sum different numbers everytime.

function sum_args(num1,num2) {
        var sum  = num1 + num2;
        console.log(sum); 
    }

    /* Now when invoking the function we can use any numbers we want: */

    sum_args(10,25); // The console will show 35

    sum_args(1000,375); // The console will show 1375

    sum_args(-2,47); // The console will show 45

The return statement

It would be good if our function could return the value so we could do anything we want with it.

function sum_args(num1,num2) {
        var sum  = num1 + num2;
        return sum; 
    }
//Now we can do anything we want with it, like using in other calculations and sending the result to an HTML element.
var average = sum_args(6,10) / 2;

    console.log( sum_args(13,21) );