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AST (Abstract Syntax Tree)The only true tool for building JavaScript
Source mapsEpic win in debugging
Source maps – epic win in debugging
Source maps – epic win in debugging
BuildersEpic fail in debugging
Builders – epic fail in debugging
umdify:
// UMD definition
output += '(function(root, factory) {\n';
output += ' if (typeof define === "function" && define.amd) {\n';
output += ' define([' + depNames.join(', ') + '], factory);\n';
output += ' } else if (typeof exports === "object") {\n';
output += ' module.exports = factory(require);\n';
…
Builders – epic fail in debugging
grunt-amd-wrap:
var srcText = grunt.file.read(file.src[0]);
var destText = amdWrap(srcText);
Builders – epic fail in debugging
gulp-concat:
buffer.push(file.contents);
…
var joinedContents = Buffer.concat(buffer);
Builders – epic fail in debugging
universal-transformer:
function transform(srcText) {
return 'var answer = 42;';
}
Your code is not a string
It has a soul
Your code has a soul
// Life, Universe, and Everything
var answer = 6 * 7;
Your code has a soul
// Life, Universe, and Everything
var answer = 6 * 7;'// Life, Universe and Everything\nvar answer = 6 * 7;'
Your code has a soul
// Life, Universe, and Everything
var answer = 6 * 7;
[
{ type: "Keyword", value: "var" },
{ type: "Identifier", value: "answer" },
{ type: "Punctuator", value: "=" },
{ type: "Numeric", value: "6" },
{ type: "Punctuator", value: "*" },
{ type: "Numeric", value: "7" },
{ type: "Punctuator", value: ";" }
]
Your code has a soul
[
{ type: "Keyword", value: "var" },
{ type: "Identifier", value: "answer" },
{ type: "Punctuator", value: "=" },
{ type: "Numeric", value: "6" },
{ type: "Punctuator", value: "*" },
{ type: "Numeric", value: "7" },
{ type: "Punctuator", value: ";" }
]
{
type: "Program",
body: [{
type: "VariableDeclaration",
declarations: [{
type: "VariableDeclarator",
id: {type: "Identifier", name: "answer"},
init: {
type: "BinaryExpression",
operator: "*",
left: {type: "Literal", value: 6},
right: {type: "Literal", value: 7}
}
}],
kind: "var"
}]
}
Your code has a soul{
type: "Program",
body: [{
type: "VariableDeclaration",
declarations: [{
type: "VariableDeclarator",
id: {type: "Identifier", name: "answer"},
init: {
type: "BinaryExpression",
operator: "*",
left: {type: "Literal", value: 6},
right: {type: "Literal", value: 7}
}
}],
kind: "var"
}]
}
Program
VariableDeclaration
VariableDeclarator
Identifier(“answer”) BinaryExpression(*)
Literal(6) Literal(7)
Your code has a soul
// Life, Universe, and Everything
var answer = 6 * 7; Program
VariableDeclaration
VariableDeclarator
Identifier(“answer”) BinaryExpression(*)
Literal(6) Literal(7)
Code toolsHow can we work with code AST?
Parsing
• JavaScript• SpiderMonkey: Reflect.parse – Mozilla's Parser API• Esprima – most popular ECMAScript parser in JS• Acorn – faster alternative ECMAScript parser in JS• UglifyJS – has own parser with custom AST format• Traceur – has ES6 parser that can be used separately as well• … (as a lot of language tools do) …
• CoffeeScript• CoffeeScriptRedux – rewrite of CS compiler that internally uses CS AST with conversion to JS
AST
• JSX• esprima-fb – Facebook's fork of Esprima Harmony branch• jsx-esprima – es* tools based JSX to JS AST transpiler
Parsing
acorn.parse('var answer = 6 * 7;', {locations: true});
// In each node.
loc: {
start: {
line: 2,
column: 0
},
end: {
line: 2,
column: 19
}
}
Linting
Querying
var found;
estraverse.traverse(tree, {
enter: function (node) {
if (node.type === 'Identifier' && node.name[0] === '_') {
found = node;
return estraverse.VisitorOption.Break;
}
}
})
Querying
require('grasp-equery')
.query('if ($cond) return $yes; else return $no;', ast)
Querying
require('grasp-squery')
.query('if[then=return][else=return]', ast)
Constructing
{ type: "Program", body: [{ type: "VariableDeclaration", declarations: [{ type: "VariableDeclarator", id: {type: "Identifier", name: "answer"}, init: { type: "BinaryExpression", operator: "*", left: {type: "Literal", value: 6}, right: {type: "Literal", value: 7} } }], kind: "var" }]}
Constructing
var b = require('ast-types').builders;
b.variableDeclaration('var', [
b.variableDeclarator(
b.identifier('answer'),
b.binaryExpression(
'*',
b.literal(6),
b.literal(7)
)
)
]);
Constructing
estemplate('var <%= varName %> = 6 * 7;', {
varName: {type: 'Identifier', name: 'answer'}
});
Transforming
var counter = 0, map = Object.create(null);
result = estraverse.replace(tree, {
enter: function (node) {
if (node.type === 'Identifier' && node.name[0] === '_')
node.name = map[node.name] || (map[node.name] = '$' + counter++);
}
});
Transforming
var Renamer = recast.Visitor.extend({
init: function () {
this.counter = 0;
this.map = Object.create(null);
},
getId: function (name) {
return this.map[name] || (this.map[name] = '$' + this.counter++);
},
visitIdentifier: function (node) {
if (node.name[0] === '_') node.name = this.getId(node.name);
}
});
Generating
var output = escodegen.generate(ast, {
sourceMap: true,
sourceMapWithCode: true
});
fs.writeFileSync('out.js', output.code);
fs.writeFileSync('out.js.map', output.map.toString());
Building with ASTWhat can we improve here?
File-based builders (Grunt)
Parsing code
Transforming AST
Generating code
Writing file
Reading file
Plugin
Transforming AST
Generating code
Parsing code
Streaming builders (Gulp, Browserify)
Reading file
Writing file
Plugin
TransformingAST
Next logical step
Reading file
Writing file
Parsing code
Generating code
Already available
astersrcwatchdestrunner
aster-parsejsesnextjsxcoffee
aster-changed
aster-concataster-equeryaster-squeryaster-rename-idsaster-traverseaster-uglifyaster-umd
npm keyword: aster-plugin
Sample build script
aster.watch(['src/**/*.js', 'src/**/*.coffee', 'src/**/*.jsx'])
.throttle(500)
.map(changed(
src => src.map(equery({
'if ($cond) return $expr1; else return $expr2;':
'return <%= cond %> ? <%= expr1 %> : <%= expr2 %>'
}))
))
.map(concat('built.js'))
.map(umd({exports: 'superLib'}))
.map(aster.dest('dist', {sourceMap: true}))
.subscribe(aster.runner);
Plugins – reactive AST transformers
module.exports = source => {
source = source || 'built.js';
return files => files
.flatMap(file => Rx.Observable.fromArray(file.program.body))
.toArray()
.map(body => ({
type: 'File',
program: {type: 'Program', body},
loc: {source}
}));
};
Integration with generic build systems
grunt.initConfig({
aster: {
options: {
equery: {
'if ($cond) return $expr1; else return $expr2;':
'return <%= cond %> ? <%= expr1 %> : <%= expr2 %>'
},
concat: 'built.js',
umd: {exports: 'superLib'},
dest: {sourceMap: true}
},
files: { 'dist': ['src/**/*.js', 'src/**/*.coffee', 'src/**/*.jsx'] }
}
});
Integration with generic build systems
gulp.src(['src/**/*.js', 'src/**/*.coffee', 'src/**/*.jsx'])
.pipe(aster(src => src
.map(equery({
'if ($cond) return $expr1; else return $expr2;':
'return <%= cond %> ? <%= expr1 %> : <%= expr2 %>'
})
.map(concat('built.js'))
.map(umd({exports: 'superLib'}))
))
.pipe(gulp.dest('dist'))
Questions?https://github.com/asterjs
@RReverserme@rreverser.com
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