BlogPost 402

I learned how to make a form input, where you don’t have to hit enter or move focus for the react app to fetch new data. First I tried creating a call to fetch in componentDidUpdate(), but this fetched to quickly whenever a user entered every character, plus after the user was done typing the page would continue fetching and refreshing until it was caught up. Maybe more importantly you may want to limit useless fetch calls.

So instead, on the event handler method for onChange, handleChange(), we change the state of the app as usual to reflect the form data, then we start a setTimout for a certain time, maybe 700 -1000 ms. Once the time expires the fetch data will call. However, we place a clearTimeOut at the very top of the handleChange() handler, so that when a user types consecutive characters the app won’t fetch until the user is done typing.

in react, the timeout function could be declared in the constructor (this.timer = undefined)

State is an object that stores data that is held by the component, to be used by the component or its child components.

Props are passed from a parent component to a child component. The data passed in props may often be data derived from state such as userId, or could be functions for children to update the parent such as this.handleChange.

ReactDOM has functions that attach React to the DOM of a browser, such as the render() which re-renders those dom elements that have been updated.

React has the main ‘guts’ of react: the class component and functional component libraries, lifecyclemethods etc.

ReactDOM is only necessary on the page where the react application renders to the index.html page for example. reactDOM.render(‘root’, <app />)

further reading: https://medium.com/programming-sage/react-vs-react-dom-a0ed3aea9745

When React was created JavaScript did not have support for classes or classical inheritance, so React created its own createClass() function to create its own system for classical inheritance.

The release of ES6 in 2015 introduced classes in JavaScript which are really of creating regular objects quickly and allow for classical inheritance.

So the difference really is to use a custom method for creating a class object or using the native ES6 way to create a class object.

The developer community has generally adopted the ES6 version which is less opaque than React.createClass();

I don’t know algorithm problem what this is referring to

I don’t know what algorithm problem this is referring to.

Event delegation means that if an event happens on an inner dom element, that event also happens to the outer dom element. This means that if you have many elements that similar behavior to clicks, you can create an eventhandler on the parent element instead of every box. This is event delegation, because the parent element is delegating this event handler to its children elements.

The element triggering the event is ‘this’ (event.currentTarget). The most deeply nested element being clicked is the event.target. So if you a <button> inside an <article> inside a window, and all three had event-handlers, one click would trigger all three. event.currentTarget would be the this (button… article… window) but the event.target in all 3 would be the most deeply nested element, the button in this case.

So if you’re using event delegation, you may need some logic to ensure that if an inner-dom element is clicked, the intended dom element is identified.

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