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Livecoding.tv Quiz of the Day: 23/11/2016

React.JS Quiz

React.JS Quiz

 

Answer:

Higher Order Components (HOCs) are the coined term for a custom Component that accepts dynamically provided children. For example, let’s make <LazyLoad /> Component that takes child image tags as children, waits until the <LazyLoad /> Component is scrolled into view, and then loads the images they point to in the background (before rendering them to the DOM).

An HOC accepts children via props:

[/crayon] Creating an HOC means handling this.props.children in the Component’s code:

interactive example can be found at https://goo.gl/ns0B6j

[/crayon] Noting a few things about this code:

  1. We set up initial state ( this.state = {loaded: 0}) in the constructor(). This will be set to 1 when the parent container is scrolled into view.
  2. The render() returns the props.children as child elements when this occurs. Extract the src by using ES6 destructuring, where {props:{src}} creates a variable src with the appropriate value.
  3. We used a single componentDidMount() lifecycle method. This is used because on mount, we’d like the component to check if the HOC is visible.
  4. The largest function of our component, _scroll(), grabs the HOC Component’s DOM element with DOM.findDOMNode() and then gets the elements position. This position is compared to the height of the browser window, and if it is less than 100px from the bottom, then the scroll listener is removed and loaded is set to 1.

This technique is called HOC (Higher Order Component) because we pass in elements as this.props.children when we nest those elements inside the container component:

[/crayon] All of these nested elements (which can be custom components) are nested under <HOC/>, thus HOC’s code will be able to access them as this.props.children.

If you want to explore more, visit our React.JS edu & tutorials section!

Below are some examples:

Restaurant Ordering App in ReactJS

CMS in ReactJS and Ruby on Rails

About author

I, Dr. Michael J. Garbade is the co-founder of the Education Ecosystem (aka LiveEdu), ex-Amazon, GE, Rebate Networks, Y-combinator. Python, Django, and DevOps Engineer. Serial Entrepreneur. Experienced in raising venture funding. I speak English and German as mother tongues. I have a Masters in Business Administration and Physics, and a Ph.D. in Venture Capital Financing. Currently, I am the Project Lead on the community project -Nationalcoronalvirus Hotline I write subject matter expert technical and business articles in leading blogs like Opensource.com, Dzone.com, Cybrary, Businessinsider, Entrepreneur.com, TechinAsia, Coindesk, and Cointelegraph. I am a frequent speaker and panelist at tech and blockchain conferences around the globe. I serve as a start-up mentor at Axel Springer Accelerator, NY Edtech Accelerator, Seedstars, and Learnlaunch Accelerator. I love hackathons and often serve as a technical judge on hackathon panels.