Expand description

EcmaScript/TypeScript parser for the rust programming language.


Heavily tested

Passes almost all tests from tc39/test262.

Error reporting

error: 'implements', 'interface', 'let', 'package', 'private', 'protected',  'public', 'static', or 'yield' cannot be used as an identifier in strict mode
 --> invalid.js:3:10
3 | function yield() {
  |          ^^^^^

Error recovery

The parser can recover from some parsing errors. For example, parser returns Ok(Module) for the code below, while emitting error to handler.

const CONST = 9000 % 2;
const enum D {
    // Comma is required, but parser can recover because of the newline.
    d = 10
    g = CONST

Example (lexer)

See lexer.rs in examples directory.

Example (parser)

extern crate swc_common;
extern crate swc_ecma_parser;
use swc_common::sync::Lrc;
use swc_common::{
    errors::{ColorConfig, Handler},
    FileName, FilePathMapping, SourceMap,
use swc_ecma_parser::{lexer::Lexer, Parser, StringInput, Syntax};

fn main() {
    let cm: Lrc<SourceMap> = Default::default();
    let handler =
        Handler::with_tty_emitter(ColorConfig::Auto, true, false,

    // Real usage
    // let fm = cm
    //     .load_file(Path::new("test.js"))
    //     .expect("failed to load test.js");
    let fm = cm.new_source_file(
        "function foo() {}".into(),
    let lexer = Lexer::new(
        // We want to parse ecmascript
        // EsVersion defaults to es5

    let mut parser = Parser::new_from(lexer);

    for e in parser.take_errors() {

    let _module = parser
        .map_err(|mut e| {
            // Unrecoverable fatal error occurred
        .expect("failed to parser module");

Cargo features


Enables typescript parser.


Verify more errors, using swc_ecma_visit.

Known issues

Null character after \

Because String of rust should only contain valid utf-8 characters while javascript allows non-utf8 characters, the parser stores invalid utf8 characters in escaped form.

As a result, swc needs a way to distinguish invalid-utf8 code points and input specified by the user. The parser stores a null character right after \\ for non-utf8 code points. Note that other parts of swc is aware of this fact.

Note that this can be changed at anytime with a breaking change.


ECMAScript lexer.

Ported from babel/babylon


Note: Lexer need access to parser’s context to lex correctly.

Syntactic context.

EcmaScript parser.

Implementation of Input.



Clone should be cheap if you are parsing typescript because typescript syntax requires backtracking.


Note: This is recommended way to parse a file.

Note: This is recommended way to parse a file.

Note: This is recommended way to parse a file.

Note: This is recommended way to parse a file.

Type Definitions


When error occurs, error is emitted and parser returns Err(()).