René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Design Meeting Notes, 8/13/2024","articleBody":"\n# Ordering Parameter Properties and Class Fields\n\nhttps://github.com/microsoft/TypeScript/issues/45995\n\n* When we adjusted our class field emit (with `useDefineForClassFields`), we also adjusted the relative ordering of class fields and parameter properties.\n* Under JS, class fields run before the body of the constructor.\n* Under TS, previously, class fields ran *after* parameter properties, but before the body of the constructor.\n* Under `useDefineForClassFields` we error on any access to parameter properties, but otherwise it's fine.\n* Should we adjust the ordering to be consistent?\n* `useDefineForClassFields` was introduced as a legacy behavior to avoid breaks, why break people?\n    * Could deprecate setting it to false.\n* We could run a PR where it always errors, see what breaks.\n    * Is there an argument for making things more spec-compliant over time?\n* Is there something clever we could do with emit?\n    * Witnessable side-effects.\n* The tough part is that most codebases that would be affected by running on GitHub won't be uncovered. Typically these are more mature codebases.\n* Could always do a codemod. We typically rely on quick fixes here.\n\n  ```ts\n  // Before\n  class A {\n      x = 1;\n      constructor(public y: number) {\n          console.log(this.y);\n      }\n  }\n  ```\n\n  ```ts\n  // After\n  class A {\n      declare x;\n      constructor(public y: number) {\n          this.x = 1;\n          console.log(this.y);\n      }\n  }\n  ```\n* Some of us feel like it's a good idea to get consistent emit. Picking a date in the future to deprecate and eventually remove is the proposed plan. But need to experiment first.\n* Maybe 6.0 deprecation is the plan.\n* This has only been available since ES2022 though!\n* 6.0 deprecation = 6.5 removal, which is just over 2 years from now.\n* Aside: we should investigate parameter properties in ECMAScript.\n","author":{"url":"https://github.com/DanielRosenwasser","@type":"Person","name":"DanielRosenwasser"},"datePublished":"2024-08-13T22:39:15Z","url":"https://github.com/microsoft/TypeScript/issues/59624"}