add ts 3.9RC

swyxio · web-flow · commit e628a10f56c6 · 2020-05-02T22:16:00.000+08:00
diff --git a/docs/advanced/patterns.md b/docs/advanced/patterns.md
@@ -380,6 +380,43 @@ handy for JSDoc users - `@public, @private, @protected, @readonly`
 
 `assumeChangesOnlyAffectDirectDependencies` reduces build times for extremely large codebases.
 
+
+## TypeScript 3.9
+
+[[Release Candidate](https://devblogs.microsoft.com/typescript/announcing-typescript-3-9-rc/)]
+
+1. (minor feature) New `ts-expect-error` directive.
+
+Use this when writing tests you expect to error. 
+
+```ts
+// @ts-expect-error
+console.log(47 * "octopus");
+```
+
+Pick `ts-expect-error` if:
+
+- you’re writing test code where you actually want the type system to error on an operation
+- you expect a fix to be coming in fairly quickly and you just need a quick workaround
+- you’re in a reasonably-sized project with a proactive team that wants to remove suppression comments as soon affected code is valid again
+
+Pick `ts-ignore` if:
+
+- you have an a larger project and and new errors have appeared in code with no clear owner
+- you are in the middle of an upgrade between two different versions of TypeScript, and a line of code errors in one version but not another.
+- you honestly don’t have the time to decide which of these options is better.
+
+2. `}` and `>` are Now Invalid JSX Text Characters
+
+They were always invalid, but now TypeScript and Babel are enforcing it:
+
+```
+Unexpected token. Did you mean `{'>'}` or `&gt;`?
+Unexpected token. Did you mean `{'}'}` or `&rbrace;`?
+```
+
+You can [convert these in bulk](https://github.com/microsoft/TypeScript/pull/37436) if needed.
+
 ## TypeScript Roadmap and Spec
 
 https://github.com/Microsoft/TypeScript/wiki/Roadmap
