This is a series of posts that will illustrate the what, why and how of Node. I'll be sharing my learnings from a course on Advanced NodeJS by Samer Buna offered on PluralSight. Any code samples tagged or attached will be available at the following repo.

Node CLI and REPL

Node CLI comes with a variety of options to expose built-in debugging, multiple ways to execute scripts and other helpful runtime options.

Running a node command without any arguments starts a REPL.

R - Read
E - Eval
P - Print
L = Loop

When in REPL, you hit enter, it reads the command, executes it, prints the result and waits for the next command.

Helpful CLI Tips and Tricks

• -c - Syntax check
• -p - Print Command. e.g node -p "process.argv.slice(1) test 42" will print ['test', '42']

Helpful Repl Tricks and Tips

• Autocomplete by Tab

• rlwrap utility to track reverse search.
  

NODE_NOREADLINE=1 rlwrap node

• _ is used to capture the last evaluated value.

• Special commands that begin with a dot.

  • .help to print all such commands.
  • .break to break out of a multiline session.
  • .load to load external script file
  • .save to save current session

• You can create your own repl with custom options by requiring a repl module and starting it with custom options. You can also control repl's global context in case of preloading a library of data.

Example below will start the repl in strict mode and doesn't print anything when result is undefined. Also, it will have lodash available globally.

  const repl = require("repl");
  const lodash = require("lodash");

  let r = repl.start({
    ignoreUndefined: true,
    replMode: repl.REPL_STRICT_MODE
  });

  r.context.lodash = lodash;