Tidy up for release

libraries/o-error/README.md

@@ -0,0 +1,76 @@
+# overleaf-error-type
+
+Make custom error types that pass `instanceof` checks, have stack traces and support custom messages and properties.
+
+The approach is based mainly on https://gist.github.com/justmoon/15511f92e5216fa2624b; it just tries to DRY it up a bit.
+
+## Usage
+
+### Define a standalone error class
+
+```js
+const errorType = require('overleaf-error-type')
+
+const CustomError = errorType.define('CustomError')
+
+function doSomethingBad () {
+  throw new CustomError()
+}
+doSomethingBad()
+// =>
+// CustomError                        <-- correct name
+//    at doSomethingBad (repl:2:9)    <-- stack trace
+```
+
+### Define an error subclass
+
+```js
+const SubCustomError = errorType.extend(CustomError, 'SubCustomError')
+
+try {
+  throw new SubCustomError()
+} catch (err) {
+  console.log(err.name) // => SubCustomError
+  console.log(err instanceof SubCustomError) // => true
+  console.log(err instanceof CustomError) // => true
+  console.log(err instanceof Error) // => true
+}
+```
+
+### Add custom message and/or properties
+
+```js
+const UserNotFoundError = errorType.define('UserNotFoundError',
+  function (userId) {
+    this.message = `User not found: ${userId}`
+    this.userId = userId
+  })
+
+throw new UserNotFoundError(123)
+// => UserNotFoundError: User not found: 123
+```
+
+### Add custom Error types under an existing class
+
+```js
+class User {
+  static lookup (userId) {
+    throw new User.UserNotFoundError(userId)
+  }
+}
+
+errorType.defineIn(User, 'UserNotFoundError', function (userId) {
+  this.message = `User not found: ${userId}`
+  this.userId = userId
+})
+
+User.lookup(123)
+// =>
+// UserNotFoundError: User not found: 123
+//    at Function.lookup (repl:3:11)
+```
+
+## References
+
+- https://gist.github.com/justmoon/15511f92e5216fa2624b
+- [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error)