Master the Art of the AST - Javascript Israel June '16

Think about the new tools that are taking over the Javascript ecosystem: Babel, Typescript, Rollup, ESLint, and smarter IDEs.
What do they all have in common: they all take Javascript source code as input, and some emit Javascript code as output.
This talk will be a deep dive into the basic building block all these tools share: Transforming your code into a JS Abstract Syntax Tree (AST).
You'll learn to read, traverse, and manipulate the AST so you can extend Babel by writing your own plugins, or by writing a custom ESLint rules to enforce your team's code conventions.
You'll also learn how to create super powerful "code-mods" to automatically convert thousands of legacy ES5 scripts to ES6 in seconds.

Transcript

2. //TODO Write linting rules to enforce your team’s code conventions Write your own javascript transpiling code Write powerful “code-mods” to automatically refactor thousands of legacy scripts from ES5 to ES6
3. //TODO Write linting rules to enforce your team’s code conventions Write your own javascript transpiling code Write powerful “code-mods” to automatically refactor thousands of legacy scripts from ES5 to ES6 ESLint jscodeshift
4. //TODO Write linting rules to enforce your team’s code conventions ESTree- based AST + Visitor Pattern Write your own javascript transpiling code Write powerful “code-mods” to automatically refactor thousands of legacy scripts from ES5 to ES6 ESLint jscodeshift
5. Yonatan Mevorach • Javascript infrastructure at • code, blog, speak, repeat blog.cowchimp.com github.com/cowchimp @cowchimp
6. Webpack Babel Uglifyjs Rollup ESLint Istanbul Ternjs jscodeshift
7. Abstract Syntax Tree http://flic.kr/p/gC4EkS cb
8. var foo = 'bar'; Program Variable Declaration Body Kind Declarations Variable Declarator Id Init Identifier Literal
9. { "type": "Program", "body": [ { "type": "VariableDeclaration", "declarations": [ { "type": "VariableDeclarator", "id": { "type": "Identifier", "name": "foo" }, "init": { "type": "Literal", "value": "bar" } } ], "kind": "var" } ] } var foo = 'bar';
10. { "type": "Program", "body": [ { "type": "VariableDeclaration", "declarations": [ { "type": "VariableDeclarator", "id": { "type": "Identifier", "name": "foo" }, "init": { "type": "Literal", "value": "bar" } } ], "kind": "var" } ] } var foo = 'bar';
11. http://flic.kr/p/3xNFue cbd Parse Traverse Manipulate Generate code I/ { O {
12. http://flic.kr/p/3xNFue cbd Parse I/ { O {
13. astexplorer.net
14. http://flic.kr/p/3xNFue cbd Traverse I/ { O {
15. ESLint
17. DEMO 1\3 and then… Questions? ESLint
18. astexplorer.net/#/bF7PLcS6GQ
19. astexplorer.net/#/rKC56tJvJJ
20. astexplorer.net/#/x9ULEp6XWw
21. http://flic.kr/p/s8G9qy cb
22. http://flic.kr/p/3xNFue cbd Manipulate I/ { O {
24. DEMO 2\3 and then… Questions?
25. astexplorer.net/#/aV9EoqGS2Q
26. astexplorer.net/#/D8mMdOO1gz
27. http://flic.kr/p/3xNFue cbd Generate code I/ { O {
28. jscodeshift
29. Babel jscodeshift Input ➡ Output Javascript ➡ Javascript Javascript ➡ Javascript Plugin-based Yes Yes Building Block AST-to-AST Transform function AST-to-AST Transform function Endorsed by Facebook Facebook http://flic.kr/p/91r3Wz cb
30. Babel jscodeshift Input ➡ Output Javascript ➡ Javascript Javascript ➡ Javascript Plugin-based Yes Yes Building Block AST-to-AST Transform function AST-to-AST Transform function Endorsed by Facebook Facebook http://flic.kr/p/91r3Wz cb Goal Compiler "Codemod" (refactoring) Example Use ES6 ➡ ES5 ES5 ➡ ES6 Output level Lower level than source Same level as source Output readability Best-effort (boilerplate code) High Usage frequency All the time One-time
31. DEMO 3\3 and then… Questions? jscodeshift
32. astexplorer.net/#/1WJItUlZFN
33. astexplorer.net/#/sAVP0oNPMd
34. github.com/cowchimp/awesome-ast blog.cowchimp.com @cowchimp yonatan@sears.co.il