Strange error in Transmission processor project

I am getting an typeError in this repl.it project in the chapter on unit testing.
here is my processor function, exactly as written in 14.5.3, requirement #2:

function processor(transmission) {
if (transmission.indexof("::") < 0) {
// data is invalid
return -1;
}
return {};
}

module.exports = processor;

and I am getting the error:
TypeError: transmission.indexof is not a function

pretty sure it is exactly as written in the syllabus and I also pretty confident my other files are correct.
Any ideas why I am getting this error?