Add Read Only Input Elements 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/).
 
-_625 TILs and counting..._
+_626 TILs and counting..._
 
 ---
 
@@ -440,6 +440,7 @@ _625 TILs and counting..._
 - [Passing Props Down To React-Router Route](react/passing-props-down-to-react-router-route.md)
 - [Proxy To An API Server In Development With CRA](react/proxy-to-an-api-server-in-development-with-cra.md)
 - [Quickly Search For A Component With React DevTools](react/quickly-search-for-a-component-with-react-devtools.md)
+- [Read Only Input Elements](react/read-only-input-elements.md)
 - [Rendering Multiple Nodes With Fragments](react/rendering-multiple-nodes-with-fragments.md)
 - [Use A Ref To Autofocus An Input](react/use-a-ref-to-autofocus-an-input.md)
 - [Visually Select A React Element For Inspection](react/visually-select-a-react-element-for-inspection.md)

react/read-only-input-elements.md

@@ -0,0 +1,31 @@
+# Read Only Input Elements
+
+Here is an input element with a `value` and no `onChange` handler.
+
+```javascript
+const MyInput = ({ value }) => {
+  return (
+    <input value={value} />
+  );
+};
+```
+
+React will raise a warning regarding the `input` element because it has a
+`value` without an `onChange` handler leaving React to wonder if it is
+intended to be a _controlled_ or _uncontrolled_ component.
+
+If our intention is to have the `value` set but not allow the user to
+directly change it, we just need to let React know that.
+
+```javascript
+const MyInput = ({ value }) => {
+  return (
+    <input readOnly value={value} />
+  );
+};
+```
+
+The `readOnly` prop means we don't intend for the input to be modified by
+user input. The React warning will now go away.
+
+h/t Dillon Hafer