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interpreters","TypeScript"],"sub_categories":[],"readme":"# engine262\n\nAn implementation of ECMA-262 in JavaScript\n\nGoals\n\n- 100% Spec Compliance\n- Introspection\n- Ease of modification\n\nNon-Goals\n\n- Speed at the expense of any of the goals\n\nThis project is bound by a [Code of Conduct][COC].\n\nJoin us in `#engine262:matrix.org`.\n\n\n## Why this exists\n\nWhile helping develop new features for JavaScript, I've found that one of the\nmost useful methods of finding what works and what doesn't is being able to\nactually run code using the new feature. [Babel][] is fantastic for this, but\nsometimes features just can't be nicely represented with it. Similarly,\nimplementing a feature in one of the engines is a large undertaking, involving\nlong compile times and annoying bugs with the optimizing compilers.\n\nengine262 is a tool to allow JavaScript developers to have a playground where new\nfeatures can be quickly prototyped and explored. As an example, adding\n[do expressions][] to this engine is as simple as the following diff:\n\n```diff\n--- a/src/evaluator.mts\n+++ b/src/evaluator.mts\n@@ -232,6 +232,8 @@ export function* Evaluate(node) {\n     case 'GeneratorBody':\n     case 'AsyncGeneratorBody':\n       return yield* Evaluate_AnyFunctionBody(node);\n+    case 'DoExpression':\n+      return yield* Evaluate_Block(node.Block);\n     default:\n       throw new OutOfRange('Evaluate', node);\n   }\n--- a/src/parser/ExpressionParser.mts\n+++ b/src/parser/ExpressionParser.mts\n@@ -579,6 +579,12 @@ export class ExpressionParser extends FunctionParser {\n         return this.parseRegularExpressionLiteral();\n       case Token.LPAREN:\n         return this.parseParenthesizedExpression();\n+      case Token.DO: {\n+        const node = this.startNode\u003cParseNode.DoExpression\u003e();\n+        this.next();\n+        node.Block = this.parseBlock();\n+        return this.finishNode(node, 'DoExpression');\n+      }\n       default:\n         return this.unexpected();\n     }\n```\n\nThis simplicity applies to many other proposals, such as [optional chaining][],\n[pattern matching][], [the pipeline operator][], and more. This engine has also\nbeen used to find bugs in ECMA-262 and [test262][], the test suite for\nconforming JavaScript implementations.\n\n## Requirements\n\nTo run engine262 itself, a engine with support for recent ECMAScript features\nis needed. Additionally, the CLI (`bin/engine262.js`) and test262 runner\n(`test/test262/test262.mts`) require a recent version of Node.js.\n\n## Using engine262\n\nYou can install it from npm.\n\n```shell\nnpm install @engine262/engine262\nyarn install @engine262/engine262\npnpm install @engine262/engine262\n```\n\nIf you install it globally, you can use the CLI like so:\n\n`$ engine262`\n\n### engine262 playground\n\n[Classic playground](https://engine262.js.org) and [Chrome Devtools style playground](https://engine262.js.org/devtools.html)\n\n### engine262 CLI\n\n#### --module/-m\n\nEvaluate the file as a module.\n\n#### --eval \\\u003cstring\u003e / -e \\\u003cstring\u003e\n\nEvaluate the given string and exit.\n\n#### --features=\\\u003cfeatureA,featureB\u003e / --features=all\n\nRun `engine262 --list-features` to see all ECMAScript features can be switched.\n\n#### --no-test262\n\nDo not expose `$` and `$262` global variable for test262 test suite.\n\n#### --no-inspector\n\nDo not start an inspector.\n\nBy default engine262 will start an inspector on `ws://localhost:9229/` (like Node.js with `--inspector`). See the [Node.js guide](https://nodejs.org/en/learn/getting-started/debugging#inspector-clients) for connecting.\n\n#### --no-preview\n\nDo not enable the preview feature in the inspector.\n\n### engine262 API\n\nSee the [example](https://github.com/engine262/engine262/blob/main/lib-src/node/example.mts).\n\n## Developing engine262\n\n`npm run build` and `npm run watch` will build and watch the build.\n\n`npm run test:test262` will run the [test262][] test suite. Run `npm run test:test262 -- --help` to see the test runner options.\n\n`npm start` start the engine262 CLI.\n\n`npm run inspector` start the website (debugging engine262 mainly happens here).\n\n## Related Projects\n\nMany people and organizations have attempted to write a JavaScript interpreter\nin JavaScript much like engine262, with different goals. Some of them are\nincluded here for reference, though engine262 is not based on any of them.\n\n- \u003chttps://github.com/NeilFraser/JS-Interpreter\u003e\n- \u003chttps://github.com/metaes/metaes\u003e\n- \u003chttps://github.com/Siubaak/sval\u003e\n\n[Babel]: https://babeljs.io/\n[COC]: https://github.com/engine262/engine262/blob/master/CODE_OF_CONDUCT.md\n[do expressions]: https://github.com/tc39/proposal-do-expressions\n[optional chaining]: https://github.com/tc39/proposal-optional-chaining\n[pattern matching]: https://github.com/tc39/proposal-pattern-matching\n[test262]: https://github.com/tc39/test262\n[the pipeline operator]: https://github.com/tc39/proposal-pipeline-operator\n","project_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fengine262%2Fengine262","html_url":"https://awesome.ecosyste.ms/projects/github.com%2Fengine262%2Fengine262","lists_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fengine262%2Fengine262/lists"}