39 lines
1.7 KiB
Markdown
39 lines
1.7 KiB
Markdown
# Typescript style guide
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## Use `type` rather than `interface` for named parameters and POJO return values.
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`type` and `interface` can be used somewhat interchangeably, but let's use `type` to describe data and `interface` to describe (polymorphic) behaviour.
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Good examples of data are option objects to have named parameters, and POJO (plain old javascript objects) without any methods, just fields.
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Also see [this playground](https://www.typescriptlang.org/play?#code/C4TwDgpgBACghgJwgO2AeTMAlge2QZygF4oBvAKCiqmTgFsIAuKfYBLZAcwG5LqATCABs4IAPzNkAVzoAjCAl4BfcuVCQoAYQAWWIfwzY8hEvCSpDuAlABkZPlQDGOITgTNW7LstWOR+QjMUYHtqKGcCNilHYDcAChxMK3xmIIsk4wBKewcoFRVyPzgArV19KAgAD2AUfkDEYNDqCM9o2IQEjIJmHT0DLvxsijCw-ClIDsSjAkzeEebjEIYAuE5oEgADABJSKeSAOloGJSgsQh29433nVwQlDbnqfKA)
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## Use `type foo = { [key: string]: any }` for types that you intend to fill in later.
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For instance, if you have a method such as:
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```js
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function load(options) {
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// ...
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}
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```
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and you intend to type options at some later point, do:
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```ts
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type Options = { [key: string]: any}
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```
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This makes it much easier to add the necessary type information at a later time.
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## Use `object` or `Record<string, any>` to describe a type that accepts any javascript object.
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Sometimes a function or method may genuinely need to accept any object; eg:
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```js
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function encodeBody(body) {
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// ...
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}
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```
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In this scenario:
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- Use `object` if you know that you will not access any property
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- Use `Record<string, any>` if you need to access some property
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Both usages prevent the type from accepting primitives (eg: string, boolean...).
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If using `Record`, ensure that you have guards to check that the properties really do exist.
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