Reagent uses async rendering which cause problems with controlled inputs. If the input element is created directly by Reagent (i.e.
[:input ...] in hiccup), a workaround can be applied, but if the input is created by JS library (i.e. JSX
<input> or React
create-element), Reagent doesn’t see the element so the workaround can’t be applied.
Due to async rendering, the DOM update doesn’t occur during the event handler, but some time later. In certain cases, like when the cursor is not at the end of the input, updating the DOM input value causes the cursor to move to the end of the input. Without async rendering, browsers probably implement logic to keep the cursor position if the value is updated during event handler.
Reagent workaround works by changing the React input element into uncontrolled input (i.e. the DOM value is not updated by React). Instead Reagent will update DOM itself if the Reagent input value property changes. This enables Reagent to check the cursor position before updating the value, and if needed, save and restore the cursor position after updating the value.
For JS libraries, usually the best solution is if the library provides an option to use custom component to create the input element, which enables Reagent to create the input element: