Check whether a string contains another string and concatenate

// Write a function that takes two strings (a and b) as arguments
// If a contains b, append b to the beginning of a
// If not, append it to the end
// Return the concatenation
function
myFunction
(
a, b
)
{

return
}
Test Cases:
myFunction('cheese', 'cake')
Expected
'cheesecake'
myFunction('lips', 's')
Expected
'slips'
myFunction('Java', 'script')
Expected
'Javascript'
myFunction(' think, therefore I am', 'I')
Expected
'I think, therefore I am'