nebu

Fast, extensible, statically typed, and light Javascript transformer. (pronounced nee-boo)

Why bother? Nebu saves developers from the slow and heavy Babel compiler. Nebu skips AST-to-code generation, preferring simple string mutations, while keeping sourcemap support. This improves performance, preserves coding style, and makes plugins less clunky.

If you need to transpile ES6+ to ES5, use Bublé after using Nebu.

If you believe in Nebu's mission, consider building a Nebu plugin. The ecosystem is practically non-existent. It needs your help! 🤓

This is still experimental! Please report bugs and contribute if you can! 🙂

Examples

See the examples folder for plugin examples.

You can test these examples like so:

git clone https://github.com/alloc/nebu
cd nebu && pnpm i
cd examples && pnpm i
./try nebu-strip-dev

Usage

const nebu = require('nebu');

nebu.process(code, {
  ast: {}, // use an existing ESTree object
  plugins: [{
    Identifier(node) {
      if (node.name == 'foo') {
        node.replace('bar')
      }
    }
  }],
})

The process function traverses the AST depth-first, which means children are visited before neighbors, and parents are visited before children.

The process function has the following options:

• ast?: object pre-existing ESTree object
• state?: object state passed to each visitor
• plugins: object[] array of visitor maps
• filename?: string path to the source code
• sourceMap?: boolean | "inline" sourcemap type
• sourceMapTarget?: string sourcemap path (relative to filename)
• generatedFile?: string path to the generated code
• includeContent?: boolean include source content in sourcemap
• jsx?: boolean enable JSX parsing

The plugins array is required. Plugins are objects whose keys are ESTree node types and each value is a function that receives the node and shared state. The plugins array supports a plugin being wrapped in {default: plugin} for ESM interop.

The state object is useful when a plugin analyzes the structure of your code and needs to communicate this information back to you. Another use case is inter-visitor communication.

The sourceMap option defaults to false, so no sourcemap is generated. Setting sourceMap to true will generate a SourceMap object and return it as the map property of the result object. Setting sourceMap to "inline" will append a //# sourceMappingURL comment to the generated code.

The includeContent option defaults to true. You must explicitly specify false to exclude source content from the sourcemap.

Utilities

The nebu/utils module exports a few utility functions you may find useful when developing a plugin.

import { findParent } from 'nebu/utils'

Node API

Every node (except the root node) has these properties:

• parent: Node the nearest container node
• ref: string the parent property that contains us

NOTE: Methods that take a code argument do not validate it for syntax errors. So be careful!

isLiteral(type)

Check if node.type equals "Literal" and typeof node.value equals the given string.

toString()

Slice the source code using node.start and node.end as boundaries.

NOTE: This does not include mutations, so the return value is static.

process(state, plugins)

Process a node with a separate set of plugins.

The state argument is optional. You may pass null or only the plugins array if your plugins are stateless.

All changes are included in the result of nebu.process.

The return value is the processed node.

walk(prop, iter)

Call the iter function for each child node that exists at the given property name. Before your function is called, the children have their parent and ref properties set accordingly. The iter argument is optional.

yield(resume)

Call the resume function after all children have been traversed. No arguments are passed. This method may be called multiple times, and by any other node.

set(prop, code)

Update some property of the node.

Properties that typically equal a Node object or an array of Node objects should be compatible with this method.

Improving the capability of this method is tracked by #8.

push(prop, code)

Append a string of code to an array of child nodes.

unshift(prop, code)

Prepend a string of code to an array of child nodes.

splice(prop, index, n, code)

Like [].splice, you can remove child nodes from an array, insert code at the given index, or both.

The n argument indicates the number of children to remove.

before(code)

Insert code before the node.

You should append a line break to code if you want it on a separate line.

after(code)

Insert code after the node.

You should prepend a line break to code if you want it on a separate line.

indent(depth)

Increase the node's indentation level.

The tab/space width is auto-detected.

The depth argument defaults to 1.

dedent(depth)

Decrease the node's indentation level.

The tab/space width is auto-detected.

The depth argument defaults to 1.

replace(code)

Replace the node with a string of code.

remove(prop)

Remove some property of the node.

When prop is undefined, remove the node entirely.