Predict the output of the following JavaScript code.

var a="javascript"; 
var x=a.lastIndexOf("a"); 
document.write(x); 

Which is a more efficient code snippet ?
Code 1 :

for(var num=10;num>=1;num–)
{
    document.writeln(num);
}

Code 2 :

var num=10;
while(num>=1)
{
    document.writeln(num);
    num++;
}

The unordered collection of properties, each of which has a name and a value is called