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Execute code each time the Node.js REPL starts

[2011-11-17] dev, nodejs, repl, javascript
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If you start the Node.js binary without any arguments, you are in the REPL (Read-Eval-Print-Loop), a JavaScript command line. This post shows you how to execute code each time the REPL starts. That allows you to, say, automatically load modules you want to use.

I have not found a way to perform the code execution via a configuration file, but you can make it happen via the following trick: Write a script that executes the code and then programmatically starts a REPL. Example: The following are the contents of a file called startnode.js.


    var repl = require("repl");
    var context = repl.start("$ ").context;
    // Configure what’s available in the REPL
    context.util = require("util");
Under Unix, the first line lets you run startnode.js as a command, if you make it executable.
    rauschma> chmod u+x startnode.js 
    rauschma> ./startnode.js
    $ util.log("hello")
    17 Nov 21:39:29 - hello
You can also use the following command to run it (with or without the first line):
    rauschma> node startnode.js
The Node.js documentation has more information on the REPL API and on commands that are available while running it. For example:
    $ .help
    .break	Sometimes you get stuck, this gets you out
    .clear	Break, and also clear the local context
    .exit	Exit the repl
    .help	Show repl options
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