Published: Modified: V1.6
node.js

The acorn javaScript parser

For some projects it might be required to parse javaScript, often doing so might be a task that is done my a javaScript engine, but sometimes I might want to parse javaScript with javaScript. A popular and well know project for doing just that is acorn which is one of many user space nodejs project that can be used for this sort of thing.

If you are new to javaScript and nodejs, or programing in general and you do not know what a parser is then maybe a brief definition of a parser is in order. I guess one way of define a parser is software that will take a string from of something and create a workable object from of it. For example say you have a text game program where a player can input a command like move up, that results in a player character in the game moving up. A parse would be the software that takes that text and creates an object maybe that contains an action property with a value of move, and a direction property with the value of up. That object is then in turn what is used to preform the action of moving up in the text only game.

1 - Getting started

When I first started writing this post the latest version of acorn was 5.3.0, however as of the latest edit of this post there is now an 8.x of this project. So if the code examples I have here break that might be a good reason why. Always check what version is being used, and not just with Acorn, often code breaking changes can be introduced into a project, and this should almost be expected when it is a new major version.

Just like any other node.js project I just created a new folder, did an npm init, and installed the latest version of acorn.

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$ mkdir test_acorn
$ cd test_acorn
$ npm init
$ npm install acorn@5.3.0 -- save
$ mkdir demos

I then also made a demos folder, and made my first demo called basic.js. It is a usual practice of mine to start out with a demo like that when trying out a project of any kind.

1.1 - Basic example of acorn

For a basic example of acorn I just want to do a kind of hello world type example. So here I am just calling thr main parser, and passing it a single line of javaScript code in string form. Then just pass the output of that to console.log to see what the result of that is.

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let acorn = require('acorn'),
 
node = acorn.parse('var n = 42;');
 
console.log(node);

When calling this script from the command line I end up getting this:

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Node {
  type: 'Program',
  start: 0,
  end: 11,
  body:
   [ Node {
       type: 'VariableDeclaration',
       start: 0,
       end: 11,
       declarations: [Array],
       kind: 'var' } ],
  sourceType: 'script' }

So acorn will give me an array of objects in a body property that is all the content of my javaScript, broken down into objects that give me useful info like the start, and end character position.

2 - Conclusion

That is it for now at least when it comes to using acorn.js. I would have worked out more examples of this package, but I think what I really need to do is start working on some kind of project in which I need a javaScript parser to begin with. So far I do find myself using parsers in real projects, it is just that so far it is only with respect to parsing markdown rather than javaScript. However I think that it does make sense to just play around with a project like this once or twitch now and then, even if it is just for the sake of gaining a sense of what there is to work with out there on the open Internet. With that said if I even need a javaScript parser in a project it would seem like this might be a decent voice for such a project.