You could write a script that opens each file and adds "use strict"\n
to the beginning of it and write it back to disk.
Very untested example:
var fs = require("fs"),
files = fs.readDirSync('./'),
i;
for (i = 0; i < files.length; i += 1) {
var fileContent = fs.readFileSync(files[i]).toString();
fileContent = "\"use strict\"\n" + fileContent;
fs.appendFileSync(files[i], fileContent);
}
Test for file[i]
being a directory and move to a function to make it recursive if you need.
Inspired by https://stackoverflow.com/a/11987281/85010 and https://stackoverflow.com/a/10559790/85010.