Var Object - Return A Var Element From Key Based?

i've seen this code at work which i do not get.

var Key = {
'Number1': 49, 'Number2': 50, 'Number3': 51, 'Number4': 52, 'Number5': 53, 'Number6': 54, 'Number7': 55,
'Number8': 56, 'Number9': 57, 'Number0': 48,
};

I need to return a var element from Key based what a var containing a string contains e.g

var string = "1"; an example

return Key.Number1

How would I do this using a for loop and not having multiple if statements