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Data structures for EcmaScript syntax trees. Includes super-fast renderer.

This is ideal for languages compiling to JavaScript. Rather than outputting a string directly, just call esast constructors and call render at the end.

See documentation here.

Get Started

npm install --save mason-lang/esast
# or:
bower install --save mason-lang/esast

To use it:

import {BinaryExpression, Literal} from 'esast/dist/ast'
import render from 'esast/dist/render'
const four = new BinaryExpression('+', new Literal(2), new Literal(2))

Source Maps

When building an AST from source code, you should attach the loc property after construction.

import {Literal} from 'esast/dist/ast'
import Loc, {Pos} from 'esast/dist/Loc'
import {renderWithSourceMap} from 'esast/dist/render'
import {loc} from 'esast/dist/util'

// Lines are 1-indexed, columns are 0-indexed.
// See `StartLine` and `StartColumn` exports of Loc.js.
const ast = loc(new Literal(5), new Loc(Pos(1, 0), Pos(1, 5)))
console.log(renderWithSourceMap(ast, 'inFileName', 'outFileName.js'))

If you're writing a compiler, you'll want to keep track of the Loc while you're lexing and later move those Locs into esast.


This converts an ast object to an esast version. You can go the other way with ast.toJSON(). This helps esast interact with other ast tools. If you want to parse, you could use acorn and do:

import {parse} from 'acorn'
import fromJson from 'esast/dist/fromJson'
const ast = fromJson(parse(src, options))

Render times

npm run perf-test
Name Render time Render time with source maps
esast 1.5ms 17ms
escodegen 7ms 120ms
esotope 2.5ms not supported

Keep in mind that fromJson takes about 6ms for this example.