Convert mm/dd/yyyy to yyyy-mm-dd

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(/(\d\d)\/(\d\d)\/(\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");

Use the split, reverse and join functions:

var yourdate = date.split("/").reverse().join("-");

The split will split the date in various parts, with / as a delimiter. The reverse function will reverse all the parts in the array, generated by the split. The join function will join all the parts back together, but now with - as a delimiter.

Edit

After reading the comments about the date being out of order: swap the second and third values of the array, created by the split function.

var dat = "03/07/2016"
var yourdate = dat.split("/").reverse();
var tmp = yourdate[2];
yourdate[2] = yourdate[1];
yourdate[1] = tmp;
yourdate = yourdate.join("-");