Incorrect ES5 transpilation for 'this' usage in lambda as a constructor default parameter

[nevedaren]

🔎 Search Terms

ES5, this alias

🕗 Version & Regression Information

• This changed between versions 5.1.6 and 5.2.2

⏯ Playground Link

https://www.typescriptlang.org/play?target=1&ts=5.2.2#code/MYGwhgzhAEDqBOYAOSCm9oG8BQ1rAHsA7CAF3gFdhSD4AKXPaANzBAEsATMU1aAXmh0KJMADNUALiwBfAJQCAfNFIALdhAB0rDt17DREuQpxMWbLj1R1M8gNyMZ2RknjtWvc7qt1SATzQAVUMpaDAiPzlpACMCAhBUcKxGPHhUUgp4IhVKVAc8JydsIlQAdzhEFHQ6OQcgA

💻 Code

// @target: es5
// @showEmit: true
class Wrapper {
 constructor(
 validate = (unsafe: {}) => this.validate(unsafe)) {
 validate({});
 }

 private validate(typeUnsafe: any): boolean {
 return true;
 }
}

new Wrapper();

Target: ES5

🙁 Actual behavior

Cannot read properties of undefined (reading 'validate') 

🙂 Expected behavior

No error (as with untranspiled version or with TS5.1.6)

Additional information about the issue

No response

[typescript-bot]

The change between v5.1.6 and v5.2.2 occurred at f9cf821.

[andrewbranch]

Ron Buckton (@rbuckton) this appears to be possibly a regression from #54505 (the repro bot just detected an emit change, so it could be a red herring)

[typescript-bot]

👋 Hi, I'm the Repro bot. I can help narrow down and track compiler bugs across releases! This comment reflects the current state of the repro in the issue body running against the nightly TypeScript.

---

Issue body code block by Anri Sidorov (@nevedaren)

👍 Compiled
Emit:

"use strict";
var Wrapper = /** @class */ (function () {
 function Wrapper(validate) {
 if (validate === void 0) { validate = function (unsafe) { return this.validate(unsafe); }; }
 validate({});
 }
 Wrapper.prototype.validate = function (typeUnsafe) {
 return true;
 };
 return Wrapper;
}());
new Wrapper();

Historical Information

Version	Reproduction Outputs
5.2.2	👍 Compiled Emit: "use strict"; var Wrapper = /** @class */ (function () { function Wrapper(validate) { if (validate === void 0) { validate = function (unsafe) { return this.validate(unsafe); }; } validate({}); } Wrapper.prototype.validate = function (typeUnsafe) { return true; }; return Wrapper; }()); new Wrapper();
4.8.2, 4.9.3, 5.0.2, 5.1.3	👍 Compiled Emit: "use strict"; var Wrapper = /** @class */ (function () { function Wrapper(validate) { if (validate === void 0) { validate = function (unsafe) { return _this.validate(unsafe); }; } var _this = this; validate({}); } Wrapper.prototype.validate = function (typeUnsafe) { return true; }; return Wrapper; }()); new Wrapper();