1> What are refs used for ?
Ans. Refs allow you to get direct access to a DOM element or an instance of a Component.
2> What happens when you call setState ?
Ans. The first thing React will do when setState is merge with object you passed into setState into the current state of the component. This will kick of a process called reconciliation.
The most efficient way possible, update the UI based on this new state.
3> When rendering a list what is a key and what is its purpose ?
Ans. Key helps React identify which items have changed, are added or are removed.
Keys should be given to the elements inside the array to give the elements a stable identity.
4> What happens during the lifecycle of a React component ?
Ans. At the highest level, React components have lifecycle events that fall into three general categories.
- State/Property Updates
5> How do you prevent the default behavior in an event callback in React ?
Ans. You call e.preventDefault(); on the event e passed into the callback.
6> What does it mean for a component to be mounted in React ?
Ans. It has a corresponding element created in the DOM and is connected to that.
7> How do you prevent a component from Rendering in Reacr ?
Ans. Return null from the render method.
8> What's the difference between a controlled component and an Uncontrolled one in React ?
Ans. This relates to stateful DOM components(form elements) and the React docs explain the difference:
A Controlled component is one the takes its current value through props and notifies the changes through callback like onChange. A parent component "controls" it by handling the callback and managing its own state and passing the new values as props to the controlled component. you can call this as a "dumb component".
A Uncontrolled Component is one that stores its own state internally, and you query the DOM using a ref to find its current value when you need it. This is a bit more like traditional HTML.
9> What is Flux ?
Ans. Unidirectional application flow paradigm/idea.
10> What is Reconciliation ?
Ans. Reconciliation is the process of comparing the DOM Tree before and after element changes and updating them accordingly.
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