Recommend return type annotation #1239
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DanielRosenwasser
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Oct 26, 2017
src/v2/guide/typescript.md
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| ## Annotating Return Type | ||
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| Vue's type definition is prone to [circular reference](https://github.com/Microsoft/TypeScript/issues/12846#issuecomment-270296195) of `this`. | ||
| Annotating return type is highly recommended to avoid such error. |
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Consider
Because of the circular nature of Vue's declaration files, TypeScript may have difficulties inferring the types of certain methods.
For this reason, you may need to annotate the return type on `computed` methods.
| return this.greet() + '!' | ||
| } | ||
| }, | ||
| // `createElement` is inferred, but `render` needs return type |
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I believe the reason you're running into this is that it references greeting. You shouldn't need this if greeting is annotated.
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I have tried it but sadly render still needs annotation. (as reported in vuejs/vue#6921).
I guess the reason is that compiler needs to check the call of createElement to get the return type, and check calling will cause check argument types. In this case, this.greeting causes cyclic error.
src/v2/guide/typescript.md
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| }) | ||
| ``` | ||
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| If you find type inference or member completion doesn't work, you can try annotating method return type. |
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If you find type inference or member completion isn't working, annotating certain methods may help address these problems.
Using the `--noImplicitAny` option will help find many of these unannotated methods.
src/v2/guide/typescript.md
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| @@ -139,3 +139,38 @@ var vm = new Vue({ | |||
| myOption: 'Hello' | |||
| }) | |||
| ``` | |||
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| ## Annotating Return Type | |||
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kazupon
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Nov 24, 2017
* Recommend return type annotation (vuejs#1239) * Recommend return type annotation * make explanation clear, thank @DanielRosenwasser * translate * update date
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Fix vuejs/vue#6921
TS has type inference limitation, we need to recommend users annotate their return type.
circular dependencymight be a hard term. So I added a link to @DanielRosenwasser 's comment.I hope this section can be clear enough for TS beginners.