Assuming your input is a string, this is easy to do using a regular expression with the String .replace() method:

var input = 03/07/2016;

var output = input.replace(/(dd)/(dd)/(d{4})/, $3-$1-$2);

Actually, if the input format is guaranteed, you could just swap the pieces around based on their position without bothering to explicitly match digits and forward slashes:

var output = input.replace(/(..).(..).(....)/, $3-$1-$2);