[javascript] Passing a local variable from one function to another

I am a beginner in JavaScript and wanted to ask the following: I have two simple functions and was wondering if there is any way to pass a variable value from one function to another. I know I can just move it outside the function to be used in other functions as well but just need to know the way how I can have one local variable and manipulate with it in my second function. Is this possible and how?

Here is some code:

window.onload = function show(){
    var x = 3;
}

function trig(){
    alert(x);
}
trig();

The question is: how do I access variable x (declared in the function show) from my second function trig?

Adding to @pranay-rana's list:

Third way is:

function passFromValue(){
    var x = 15;
    return x;  
}
function passToValue() {
    var y = passFromValue();
    console.log(y);//15
}
passToValue(); 

First way is

function function1()
{
  var variable1=12;
  function2(variable1);
}

function function2(val)
{
  var variableOfFunction1 = val;

// Then you will have to use this function for the variable1 so it doesn't really help much unless that's what you want to do. }

Second way is

var globalVariable;
function function1()
{
  globalVariable=12;
  function2();
}

function function2()
{
  var local = globalVariable;
}

You can very easily use this to re-use the value of the variable in another function.

// Use this in source window.var1= oEvent.getSource().getBindingContext();

// Get value of var1 in destination var var2= window.var1;