Edit in JSFiddle

var num1 = 10;
var num2 = num1;
num2 = 20;
document.write('num1 = ' + num1 + '<br>');
document.write('num2 = ' + num2 + '<br>');
document.write('<br>');

var arr1 = [10,20,30];
var arr2 = arr1;
arr2[1] = 50;
document.write("arr1 = " + arr1 + "<br>" );
document.write("arr2 = " + arr2 + "<br>" );