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<!doctype html>
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<h1>Node.js v0.10.29 Manual & Documentation</h1>
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<h2>Table of Contents</h2>
<ul>
<li><a href="#repl_repl">REPL</a><ul>
<li><a href="#repl_repl_start_options">repl.start(options)</a><ul>
<li><a href="#repl_event_exit">Event: 'exit'</a></li>
</ul>
</li>
<li><a href="#repl_repl_features">REPL Features</a></li>
</ul>
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<div id="apicontent">
<h1>REPL<span><a class="mark" href="#repl_repl" id="repl_repl">#</a></span></h1>
<p>A Read-Eval-Print-Loop (REPL) is available both as a standalone program and
easily includable in other programs. The REPL provides a way to interactively
run JavaScript and see the results. It can be used for debugging, testing, or
just trying things out.
</p>
<p>By executing <code>node</code> without any arguments from the command-line you will be
dropped into the REPL. It has simplistic emacs line-editing.
</p>
<pre><code>mjr:~$ node
Type '.help' for options.
> a = [ 1, 2, 3];
[ 1, 2, 3 ]
> a.forEach(function (v) {
... console.log(v);
... });
1
2
3</code></pre>
<p>For advanced line-editors, start node with the environmental variable
<code>NODE_NO_READLINE=1</code>. This will start the main and debugger REPL in canonical
terminal settings which will allow you to use with <code>rlwrap</code>.
</p>
<p>For example, you could add this to your bashrc file:
</p>
<pre><code>alias node="env NODE_NO_READLINE=1 rlwrap node"</code></pre>
<h2>repl.start(options)<span><a class="mark" href="#repl_repl_start_options" id="repl_repl_start_options">#</a></span></h2>
<p>Returns and starts a <code>REPLServer</code> instance. Accepts an "options" Object that
takes the following values:
</p>
<ul>
<li><p><code>prompt</code> - the prompt and <code>stream</code> for all I/O. Defaults to <code>> </code>.</p>
</li>
<li><p><code>input</code> - the readable stream to listen to. Defaults to <code>process.stdin</code>.</p>
</li>
<li><p><code>output</code> - the writable stream to write readline data to. Defaults to
<code>process.stdout</code>.</p>
</li>
<li><p><code>terminal</code> - pass <code>true</code> if the <code>stream</code> should be treated like a TTY, and
have ANSI/VT100 escape codes written to it. Defaults to checking <code>isTTY</code>
on the <code>output</code> stream upon instantiation.</p>
</li>
<li><p><code>eval</code> - function that will be used to eval each given line. Defaults to
an async wrapper for <code>eval()</code>. See below for an example of a custom <code>eval</code>.</p>
</li>
<li><p><code>useColors</code> - a boolean which specifies whether or not the <code>writer</code> function
should output colors. If a different <code>writer</code> function is set then this does
nothing. Defaults to the repl's <code>terminal</code> value.</p>
</li>
<li><p><code>useGlobal</code> - if set to <code>true</code>, then the repl will use the <code>global</code> object,
instead of running scripts in a separate context. Defaults to <code>false</code>.</p>
</li>
<li><p><code>ignoreUndefined</code> - if set to <code>true</code>, then the repl will not output the
return value of command if it's <code>undefined</code>. Defaults to <code>false</code>.</p>
</li>
<li><p><code>writer</code> - the function to invoke for each command that gets evaluated which
returns the formatting (including coloring) to display. Defaults to
<code>util.inspect</code>.</p>
</li>
</ul>
<p>You can use your own <code>eval</code> function if it has following signature:
</p>
<pre><code>function eval(cmd, context, filename, callback) {
callback(null, result);
}</code></pre>
<p>Multiple REPLs may be started against the same running instance of node. Each
will share the same global object but will have unique I/O.
</p>
<p>Here is an example that starts a REPL on stdin, a Unix socket, and a TCP socket:
</p>
<pre><code>var net = require("net"),
repl = require("repl");
connections = 0;
repl.start({
prompt: "node via stdin> ",
input: process.stdin,
output: process.stdout
});
net.createServer(function (socket) {
connections += 1;
repl.start({
prompt: "node via Unix socket> ",
input: socket,
output: socket
}).on('exit', function() {
socket.end();
})
}).listen("/tmp/node-repl-sock");
net.createServer(function (socket) {
connections += 1;
repl.start({
prompt: "node via TCP socket> ",
input: socket,
output: socket
}).on('exit', function() {
socket.end();
});
}).listen(5001);</code></pre>
<p>Running this program from the command line will start a REPL on stdin. Other
REPL clients may connect through the Unix socket or TCP socket. <code>telnet</code> is useful
for connecting to TCP sockets, and <code>socat</code> can be used to connect to both Unix and
TCP sockets.
</p>
<p>By starting a REPL from a Unix socket-based server instead of stdin, you can
connect to a long-running node process without restarting it.
</p>
<p>For an example of running a "full-featured" (<code>terminal</code>) REPL over
a <code>net.Server</code> and <code>net.Socket</code> instance, see: <a href="https://gist.github.com/2209310">https://gist.github.com/2209310</a>
</p>
<p>For an example of running a REPL instance over <code>curl(1)</code>,
see: <a href="https://gist.github.com/2053342">https://gist.github.com/2053342</a>
</p>
<h3>Event: 'exit'<span><a class="mark" href="#repl_event_exit" id="repl_event_exit">#</a></span></h3>
<p><code>function () {}</code>
</p>
<p>Emitted when the user exits the REPL in any of the defined ways. Namely, typing
<code>.exit</code> at the repl, pressing Ctrl+C twice to signal SIGINT, or pressing Ctrl+D
to signal "end" on the <code>input</code> stream.
</p>
<p>Example of listening for <code>exit</code>:
</p>
<pre><code>r.on('exit', function () {
console.log('Got "exit" event from repl!');
process.exit();
});</code></pre>
<h2>REPL Features<span><a class="mark" href="#repl_repl_features" id="repl_repl_features">#</a></span></h2>
<!-- type=misc -->
<p>Inside the REPL, Control+D will exit. Multi-line expressions can be input.
Tab completion is supported for both global and local variables.
</p>
<p>The special variable <code>_</code> (underscore) contains the result of the last expression.
</p>
<pre><code>> [ "a", "b", "c" ]
[ 'a', 'b', 'c' ]
> _.length
3
> _ += 1
4</code></pre>
<p>The REPL provides access to any variables in the global scope. You can expose
a variable to the REPL explicitly by assigning it to the <code>context</code> object
associated with each <code>REPLServer</code>. For example:
</p>
<pre><code>// repl_test.js
var repl = require("repl"),
msg = "message";
repl.start("> ").context.m = msg;</code></pre>
<p>Things in the <code>context</code> object appear as local within the REPL:
</p>
<pre><code>mjr:~$ node repl_test.js
> m
'message'</code></pre>
<p>There are a few special REPL commands:
</p>
<ul>
<li><code>.break</code> - While inputting a multi-line expression, sometimes you get lost
or just don't care about completing it. <code>.break</code> will start over.</li>
<li><code>.clear</code> - Resets the <code>context</code> object to an empty object and clears any
multi-line expression.</li>
<li><code>.exit</code> - Close the I/O stream, which will cause the REPL to exit.</li>
<li><code>.help</code> - Show this list of special commands.</li>
<li><code>.save</code> - Save the current REPL session to a file<blockquote>
<p>.save ./file/to/save.js</p>
</blockquote>
</li>
<li><code>.load</code> - Load a file into the current REPL session.<blockquote>
<p>.load ./file/to/load.js</p>
</blockquote>
</li>
</ul>
<p>The following key combinations in the REPL have these special effects:
</p>
<ul>
<li><code><ctrl>C</code> - Similar to the <code>.break</code> keyword. Terminates the current
command. Press twice on a blank line to forcibly exit.</li>
<li><code><ctrl>D</code> - Similar to the <code>.exit</code> keyword.</li>
</ul>
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