Shifting all the values in an array one index higher with the displaced last element placed as the first element

Question

I'm struggling with the below code in JS please help:

Currently trying to get

[20,30,40,50]

to be

[50,20,30,40]

any tips?

Here is the code I have so far below!

// A program to shift all the values in an array one index higher, with the displaced last element being placed as the first element

var test = [20,30,40,50];

for (i=0; i<test.length;i++)
{
    alert(test[i] + " is currently index: " + [i]); 
    }

test[0] = test[test.length-1];

for (i=0; i<test.length;i++)
{
    alert(test[i] + " is now index: " + [i+1]); 
    }

Answer 1

Just do this:

a.unshift(a.pop());