Follow the instructions to get asciiflow running locally.

Compile the javascript:
~/asciiflow2$ ./compile.sh

If you get a permissions error:
~/asciiflow2$ chmod a+x closure-compiler.jar

Run a simple web server:
~/asciiflow2$ python -m http.server

Or, if you're a debian user and still believe that python 2 is up-to-date:
~/asciiflow2$ python -m SimpleHTTPServer

Goto: http://localhost:8000/index.html

When developing, use the Google JS linter, gjslint.

BONUS:
put the following in your .bashrc:
alias asciiflow="bash -c 'cd yourasciiflowfolder && ./compile.sh && python -m http.server'"

then
source .bashrc

;)