Add Enforce Specific Values With PropTypes as a react til

README.md

@@ -10,7 +10,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 For a steady stream of TILs from a variety of rocketeers, checkout
 [til.hashrocket.com](https://til.hashrocket.com/).
 
-_650 TILs and counting..._
+_651 TILs and counting..._
 
 ---
 
@@ -451,6 +451,7 @@ _650 TILs and counting..._
 - [Destructure Variables As Props To A Component](react/destructure-variables-as-props-to-a-component.md)
 - [Dispatch Anywhere With Redux](react/dispatch-anywhere-with-redux.md)
 - [Dynamically Add Props To A Child Component](react/dynamically-add-props-to-a-child-component.md)
+- [Enforce Specific Values With PropTypes](react/enforce-specific-values-with-proptypes.md)
 - [Force A Component To Only Have One Child](react/force-a-component-to-only-have-one-child.md)
 - [Inactive And Active Component Styles With Radium](react/inactive-and-active-component-styles-with-radium.md)
 - [Inline Style Attributes Should Be Camel Cased](react/inline-style-attributes-should-be-camel-cased.md)

react/enforce-specific-values-with-proptypes.md

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+# Enforce Specific Values With PropTypes
+
+Being able to constrain our user interfaces to very specific values is
+valuable. This makes our interfaces easier to reason about and easier to
+test. PropTypes in general are one of the ways that we constrain our UIs. We
+can go even further than simple type constraints by limiting a prop to a
+specific set of values, an enum if you will.
+
+```javascript
+MyComponent.propTypes = {
+  flavors: PropTypes.oneOf(['Vanilla', 'Chocolate', 'Strawberry']),
+};
+```
+
+The docs say about `oneOf()`:
+
+> You can ensure that your prop is limited to specific values by treating it
+> as an enum.
+
+If we use `MyComponent` with a value such as `Pistachio`, we'll have a
+console warning to answer for.
+
+[source](https://reactjs.org/docs/typechecking-with-proptypes.html)