Learn React with TypeScript 3

Triggering validation rule execution from field

When the user fills in the form, we want the validation rules to trigger when a field loses focus. We'll implement this in this section:

1. Let's create a function that is going to handle the blur event for all three of the different editors:

const handleChange = (  ...};const handleBlur = (  e:    | React.FocusEvent<HTMLInputElement>    | React.FocusEvent<HTMLTextAreaElement>    | React.FocusEvent<HTMLSelectElement>,  context: IFormContext) => {  if (context.validate) {    context.validate(props.name, e.currentTarget.value);  }};return ( ... )

• The TypeScript blur event type is FocusEvent<T>, where T is the type of the element that is being handled.
• The handler's first parameter, e, is the React blur event handler ...