A Read-Eval-Print-Loop (REPL) is available both as a standalone program and\neasily includable in other programs. The REPL provides a way to interactively\nrun JavaScript and see the results. It can be used for debugging, testing, or\njust trying things out.\n\n
\nBy executing node without any arguments from the command-line you will be\ndropped into the REPL. It has simplistic emacs line-editing.\n\n
mjr:~$ node\nType '.help' for options.\n> a = [ 1, 2, 3];\n[ 1, 2, 3 ]\n> a.forEach(function (v) {\n... console.log(v);\n... });\n1\n2\n3For advanced line-editors, start node with the environmental variable\nNODE_NO_READLINE=1. This will start the main and debugger REPL in canonical\nterminal settings which will allow you to use with rlwrap.\n\n
For example, you could add this to your bashrc file:\n\n
\nalias node="env NODE_NO_READLINE=1 rlwrap node"Returns and starts a REPLServer instance. Accepts an "options" Object that\ntakes the following values:\n\n
prompt - the prompt and stream for all I/O. Defaults to > .
input - the readable stream to listen to. Defaults to process.stdin.
output - the writable stream to write readline data to. Defaults to\nprocess.stdout.
terminal - pass true if the stream should be treated like a TTY, and\nhave ANSI/VT100 escape codes written to it. Defaults to checking isTTY\non the output stream upon instantiation.
eval - function that will be used to eval each given line. Defaults to\nan async wrapper for eval(). See below for an example of a custom eval.
useColors - a boolean which specifies whether or not the writer function\nshould output colors. If a different writer function is set then this does\nnothing. Defaults to the repl's terminal value.
useGlobal - if set to true, then the repl will use the global object,\ninstead of running scripts in a separate context. Defaults to false.
ignoreUndefined - if set to true, then the repl will not output the\nreturn value of command if it's undefined. Defaults to false.
writer - the function to invoke for each command that gets evaluated which\nreturns the formatting (including coloring) to display. Defaults to\nutil.inspect.
You can use your own eval function if it has following signature:\n\n
function eval(cmd, context, filename, callback) {\n callback(null, result);\n}Multiple REPLs may be started against the same running instance of node. Each\nwill share the same global object but will have unique I/O.\n\n
\nHere is an example that starts a REPL on stdin, a Unix socket, and a TCP socket:\n\n
\nvar net = require("net"),\n repl = require("repl");\n\nconnections = 0;\n\nrepl.start({\n prompt: "node via stdin> ",\n input: process.stdin,\n output: process.stdout\n});\n\nnet.createServer(function (socket) {\n connections += 1;\n repl.start({\n prompt: "node via Unix socket> ",\n input: socket,\n output: socket\n }).on('exit', function() {\n socket.end();\n })\n}).listen("/tmp/node-repl-sock");\n\nnet.createServer(function (socket) {\n connections += 1;\n repl.start({\n prompt: "node via TCP socket> ",\n input: socket,\n output: socket\n }).on('exit', function() {\n socket.end();\n });\n}).listen(5001);Running this program from the command line will start a REPL on stdin. Other\nREPL clients may connect through the Unix socket or TCP socket. telnet is useful\nfor connecting to TCP sockets, and socat can be used to connect to both Unix and\nTCP sockets.\n\n
By starting a REPL from a Unix socket-based server instead of stdin, you can\nconnect to a long-running node process without restarting it.\n\n
\nFor an example of running a "full-featured" (terminal) REPL over\na net.Server and net.Socket instance, see: https://gist.github.com/2209310\n\n
For an example of running a REPL instance over curl(1),\nsee: https://gist.github.com/2053342\n\n
function () {}\n\n
Emitted when the user exits the REPL in any of the defined ways. Namely, typing\n.exit at the repl, pressing Ctrl+C twice to signal SIGINT, or pressing Ctrl+D\nto signal "end" on the input stream.\n\n
Example of listening for exit:\n\n
r.on('exit', function () {\n console.log('Got "exit" event from repl!');\n process.exit();\n});Inside the REPL, Control+D will exit. Multi-line expressions can be input.\nTab completion is supported for both global and local variables.\n\n
\nThe special variable _ (underscore) contains the result of the last expression.\n\n
> [ "a", "b", "c" ]\n[ 'a', 'b', 'c' ]\n> _.length\n3\n> _ += 1\n4The REPL provides access to any variables in the global scope. You can expose\na variable to the REPL explicitly by assigning it to the context object\nassociated with each REPLServer. For example:\n\n
// repl_test.js\nvar repl = require("repl"),\n msg = "message";\n\nrepl.start().context.m = msg;Things in the context object appear as local within the REPL:\n\n
mjr:~$ node repl_test.js\n> m\n'message'There are a few special REPL commands:\n\n
\n.break - While inputting a multi-line expression, sometimes you get lost\nor just don't care about completing it. .break will start over..clear - Resets the context object to an empty object and clears any\nmulti-line expression..exit - Close the I/O stream, which will cause the REPL to exit..help - Show this list of special commands..save - Save the current REPL session to a file\n\n.save ./file/to/save.js
\n
.load - Load a file into the current REPL session.\n\n.load ./file/to/load.js
\n
The following key combinations in the REPL have these special effects:\n\n
\n<ctrl>C - Similar to the .break keyword. Terminates the current\ncommand. Press twice on a blank line to forcibly exit.<ctrl>D - Similar to the .exit keyword.