sveltejsesrap
Parse in reverse. AST goes in, code comes out.
Usage
import { print } from 'esrap';
import ts from 'esrap/languages/ts';
const ast = {
type: 'Program',
body: [
{
type: 'ExpressionStatement',
expression: {
callee: {
type: 'Identifier',
name: 'alert'
},
arguments: [
{
type: 'Literal',
value: 'hello world!'
}
]
}
}
]
};
const { code, map } = print(ast, ts());
console.log(code); // alert('hello world!');If the nodes of the input AST have loc properties (e.g. the AST was generated with acorn with the locations option set), sourcemap mappings will be created.
Built-in languages
esrap ships with two built-in languages — ts() and tsx() (considered experimental at present!) — which can print ASTs conforming to @typescript-eslint/types (which extends ESTree):
import ts from 'esrap/languages/ts';
import tsx from 'esrap/languages/tsx'; // experimental!Both languages accept an options object:
const { code, map } = print(
ast,
ts({
// how string literals should be quoted — `single` (the default) or `double`
quotes: 'single',
// an array of `{ type: 'Line' | 'Block', value: string, loc: { start, end } }` objects
comments: []
})
);You can generate the comments array by, for example, using Acorn's onComment option.
Custom languages
You can also create your own languages:
import { print, type Visitors } from 'esrap';
const language: Visitors<MyNodeType> = {
_(node, context, visit) {
// the `_` visitor handles any node type
context.write('[');
visit(node);
context.write(']');
},
List(node, context) {
// node.type === 'List'
for (const child of node.children) {
context.visit(child);
}
},
Foo(node, context) {
// node.type === 'Foo'
context.write('foo');
},
Bar(node, context) {
// node.type === 'Bar'
context.write('bar');
}
};
const ast: MyNodeType = {
type: 'List',
children: [{ type: 'Foo' }, { type: 'Bar' }]
};
const { code, map } = print(ast, language);
code; // `[[foo][bar]]`The context API has several methods:
context.write(data: string, node?: BaseNode)— add a string. Ifnodeis provided and has a standardlocproperty (withstartandendproperties each with alineandcolumn), a sourcemap mapping will be createdcontext.indent()— increase the indentation level, typically before adding a newlinecontext.newline()— self-explanatorycontext.margin()— causes the next newline to be repeated (consecutive newlines are otherwise merged into one)context.dedent()— decrease the indentation level (again, typically before adding a newline)context.visit(node: BaseNode)— calls the visitor corresponding tonode.typecontext.location(line: number, column: number)— insert a sourcemap mapping without callingcontext.write(...)context.measure()— returns the number of characters contained incontextcontext.empty()— returns true if the context has no contentcontext.new()— creates a child contextcontext.append(child)— appends a child context
In addition, context.multiline is true if the context has multiline content. (This is useful for knowing, for example, when to insert newlines between nodes.)
To understand how to wield these methods effectively, read the source code for the built-in languages.
Options
You can pass the following options:
const { code, map } = print(ast, ts(), {
// Populate the `sources` field of the resulting sourcemap
// (note that the AST is assumed to come from a single file)
sourceMapSource: 'input.js',
// Populate the `sourcesContent` field of the resulting sourcemap
sourceMapContent: fs.readFileSync('input.js', 'utf-8'),
// Whether to encode the `mappings` field of the resulting sourcemap
// as a VLQ string, rather than an unencoded array. Defaults to `true`
sourceMapEncodeMappings: false,
// String to use for indentation — defaults to '\t'
indent: ' '
});Why not just use Prettier?
Because it's ginormous.
Developing
This repo uses pnpm. Once it's installed, do pnpm install to install dependencies, and pnpm test to run the tests.