ASTs & Ember.js

About me

twitter/rajasegar_c

Front-end Developer @ Freshworks

github/rajasegar

hangaroundtheweb.com

What is an AST?

a tree representation of the abstract syntactic structure of source code written in a programming language.

An AST is basically a DOM for your code.

Lexical Analyzer

Scanner

function helloWorld() {
    console.log('hello world');
}

Syntax Analyzer

Parser

function helloWorld() {
    console.log('hello world');
}

{
  "type": "Program",
  "start": 0,
  "end": 44,
  "body": [
    {
      "type": "FunctionDeclaration",
      "start": 0,
      "end": 44,
      "id": {
        "type": "Identifier",
        "start": 9,
        "end": 14,
        "name": "hello"
      },
      "expression": false,
      "generator": false,
      "params": [],
      "body": {
        "type": "BlockStatement",
        "start": 17,
        "end": 44,
        "body": [
          {
            "type": "ExpressionStatement",
            "start": 21,
            "end": 42,
            "expression": {
              "type": "CallExpression",
              "start": 21,
              "end": 41,
              "callee": {
                "type": "MemberExpression",
                "start": 21,
                "end": 32,
                "object": {
                  "type": "Identifier",
                  "start": 21,
                  "end": 28,
                  "name": "console"
                },
                "property": {
                  "type": "Identifier",
                  "start": 29,
                  "end": 32,
                  "name": "log"
                },
                "computed": false
              },
              "arguments": [
                {
                  "type": "Literal",
                  "start": 33,
                  "end": 40,
                  "value": "hello",
                  "raw": "'hello'"
                }
              ]
            }
          }
        ]
      }
    }
  ],
  "sourceType": "module"
}

AST

Where is it used?

Syntax Highlighting
Code Completion
Static Analysis (aka ESLint, etc.,)
Code Coverage
Minification
JIT Compilation
Source Maps
Compiling to JS languages
Code Refactoring & Migrations
And much more ...

Code Transformations

Babel

Glimmer Compiler

Codemods

recast

https://github.com/benjamn/recast

const recast = require('recast');
const code = fs.readFileSync('code.js','utf-8');
const ast = recast.parse(code);
const faster = transform(ast);
const output = recast.print(faster).code;

/**
 * This replaces every occurrence of variable "foo".
 */
module.exports = function(fileInfo, api) {
  return api.jscodeshift(fileInfo.source)
    .findVariableDeclarators('foo')
    .renameTo('bar')
    .toSource();
}

jscodeshift

https://github.com/facebook/jscodeshift

AST Explorer

http://astexplorer.net

codemod-cli

a tool for generating, testing, and publishing codemods.

https://github.com/rwjblue/codemod-cli

#topic-codemods

Ember Discord Channel

Time to

apply what we learned!

The "D" word

DOCUMENTATION

Writing

react-docgen

react-styleguidist

ember-cli-addon-docs

Ember

React