从函数内改变全局变量

Question

Here im having a bit of an issue with this very simple script Ive written up. The aim for this script is to simply reduce the given number by one each time the button is clicked. I cannot appear to do this.. My global variable being the Number=100 doesnt appear to change, or change more than once.. Apologies for not being able to explain this well. Here is the part im working on..:

<script>
  var Number = 100;        // Number i want changed and to keep changing each button click
  function outcome() {     // Button calls this function
    Number = Number - 1;   // Tries to change Global Number.. :/
  }
  document.write(Number);  // Has the Number written in the document
</script> 

Answer 1

Yes, conceptually this is right. Only you are not calling the function, at least not before writing Number to the document.

Btw, Number is the global reference to the Number constructor so you should use another variable name, lowercase at best.

var num = 100;
function outcome() {
    num--;
}
outcome();
document.write(num); // 99

or

<script>
var num = 100;
function outcome() {
    num--;
    alert(num);
}
</script>
<button onclick="outcome()">Decrease!</button>

( Demo at jsfiddle.net )

Answer 2

You have to call your function:

<script>
var Number=100    
function outcome(){ 
Number=Number-1 
}
outcome(); // call the function here
document.write(Number)  
</script> 

or don't use a function in the first place:

<script>
var Number=100    
Number=Number-1   
document.write(Number) 
</script>