Read OPF files with JS

Question

I want to open an OPF file using Javascript. I want to create an Epub reade in JS but first I need to reed that file. It's an XML file with .opf extension. I need to read the tags inside that file, but I don't know how to do that.
EDIT:
I found something. Everyone that uses FileReader get the "file" object from an input file, but I want to read a local file in my server. How can I get that file?

var reader = new FileReader();
reader.readAstext(file)

Answer 1

I changed method. Now I use PHP xmldomelement.