{ "source": "doc/api/repl.markdown", "modules": [ { "textRaw": "REPL", "name": "repl", "desc": "

A Read-Eval-Print-Loop (REPL) is available both as a standalone program and easily\nincludable in other programs. REPL provides a way to interactively run\nJavaScript and see the results. It can be used for debugging, testing, or\njust trying things out.\n\n

\n

By executing node without any arguments from the command-line you will be\ndropped into the REPL. It has simplistic emacs line-editing.\n\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\n3
\n

For advanced line-editors, start node with the environmental variable NODE_NO_READLINE=1.\nThis will start the REPL in canonical terminal settings which will allow you to use with rlwrap.\n\n

\n

For example, you could add this to your bashrc file:\n\n

\n
alias node="env NODE_NO_READLINE=1 rlwrap node"
\n", "methods": [ { "textRaw": "repl.start([prompt], [stream], [eval], [useGlobal], [ignoreUndefined])", "type": "method", "name": "start", "desc": "

Starts a REPL with prompt as the prompt and stream for all I/O. prompt\nis optional and defaults to > . stream is optional and defaults to\nprocess.stdin. eval is optional too and defaults to async wrapper for\neval().\n\n

\n

If useGlobal is set to true, then the repl will use the global object,\ninstead of running scripts in a separate context. Defaults to false.\n\n

\n

If ignoreUndefined is set to true, then the repl will not output return value\nof command if it's undefined. Defaults to false.\n\n

\n

You can use your own eval function if it has following signature:\n\n

\n
function eval(cmd, callback) {\n  callback(null, result);\n}
\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

\n

Here is an example that starts a REPL on stdin, a Unix socket, and a TCP socket:\n\n

\n
var net = require("net"),\n    repl = require("repl");\n\nconnections = 0;\n\nrepl.start("node via stdin> ");\n\nnet.createServer(function (socket) {\n  connections += 1;\n  repl.start("node via Unix socket> ", socket);\n}).listen("/tmp/node-repl-sock");\n\nnet.createServer(function (socket) {\n  connections += 1;\n  repl.start("node via TCP socket> ", socket);\n}).listen(5001);
\n

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

\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\n

\n", "signatures": [ { "params": [ { "name": "prompt", "optional": true }, { "name": "stream", "optional": true }, { "name": "eval", "optional": true }, { "name": "useGlobal", "optional": true }, { "name": "ignoreUndefined", "optional": true } ] } ] } ], "miscs": [ { "textRaw": "REPL Features", "name": "REPL Features", "type": "misc", "desc": "

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

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The special variable _ (underscore) contains the result of the last expression.\n\n

\n
> [ "a", "b", "c" ]\n[ 'a', 'b', 'c' ]\n> _.length\n3\n> _ += 1\n4
\n

The 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

\n
// repl_test.js\nvar repl = require("repl"),\n    msg = "message";\n\nrepl.start().context.m = msg;
\n

Things in the context object appear as local within the REPL:\n\n

\n
mjr:~$ node repl_test.js\n> m\n'message'
\n

There are a few special REPL commands:\n\n

\n\n

The following key combinations in the REPL have these special effects:\n\n

\n\n" } ], "type": "module", "displayName": "REPL" } ] }