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HTML

              
                <div id="app">
</div>
              
            
!

CSS

              
                :root {
  --objectFit: none;
	 --containerWidth: 500px;
	 --containerHeight: 281px;
	
/* 	 Colors */
	--turquoise-dark: #0e8873;
	--turquoise-light: #59c5af;
	--yellow-light: #fcf9ec;
	--green: #67eaca;
	
/* 	font-size */
	--fs-s: 1.4rem;
	--fs-m: 1.6rem;
}

@media (max-width: 450px) {
	:root {
		--containerWidth: 100%;
	}
}

html {
	font-size: 62.5%;
}

body {
	font-family: 'Roboto', sans-serif;
 font-weight: 300;
	font-size: var(--fs-m);
	line-height: 1.5;
	background-color: var(--yellow-light);
	color: #212020;
}

h1, h2 {
 font-family: 'Roboto Slab', serif;
}

.wrapper {
  display: grid;
  grid-gap: 1.6rem;
  padding: 1.6rem;
	 max-width: 900px;
		margin: auto;
}

.image-container {
  width: var(--containerWidth);
  height: var(--containerHeight);
	 justify-self: center;
	 background-color: #212020;
	 border: 2px solid #212020;
}
.image {
  width: 100%;
  height: 100%;
  object-fit: var(--objectFit);
}

.image-width-container,
.image-aspect-ratio-container,
.object-fit-container,
.container-aspect-ratio {
	display: grid;
	grid-template-rows: 1fr 4rem;
	grid-gap: 0.8rem;
	font-weight: 500;
}

.form-container {
		display: grid;
		grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
	 grid-gap: 1.6rem;
}
.title {
	 margin: 0;
	 text-align: center;
	 line-height: 1.2;
	 color: var(--turquoise-dark);
}
.description {
	 margin: 0;
	 font-style: italic;
}

.select-field,
.input-field {
		background-color: var(--yellow-light);
	 border: 2px solid var(--turquoise-light);
		padding: 0.8rem;
	 min-width: 10rem;
}
.select-field:hover, 
.input-field:hover {
	border-color: var(--turquoise-dark)
}
	select {
  -webkit-appearance: none;
  -webkit-border-radius: 0px;
}

              
            
!

JS

              
                const objectFitOptions = ["fill", "cover", "contain", "none", "scale-down"]

function getMultiplier (aspectRatio) {
	let multiplier;
	 switch(aspectRatio) {
				case "16-9":
					return multiplier = 9/16
						break;
				case "3-4":
				return multiplier = 4/3
						break;
				case "3-2":
				return multiplier = 2/3
						break;
				case "4-3":
				return multiplier = 3/4
						break;
				case "1-1":
				return multiplier = 1/1
						break;
				default:
				return multiplier = 9/16
		}
}

const ObjectFit = ({onChange, value}) => {
  return (
    <div class="object-fit-container">
      <label htmlFor="object-fit">Object-fit</label>
    <select id="object-fit" class="select-field" value={value} onChange={onChange}>
      <option value="">Select</option>
      {objectFitOptions.map(option => <option value={option}>{option}</option> )}
    </select>
    </div>
  )
}

const ImageAspectRatio = ({onChange, imageAspectRatio}) => {
  return (
    <div class="image-aspect-ratio-container">
      <label htmlFor="image-aspect-ratio">Image Aspect ratio</label>
    <select id="image-aspect-ratio" class="select-field" value={imageAspectRatio} onChange={onChange}>
      <option value="16-9">16:9</option>
      <option value="3-4">3:4</option>
      <option value="1-1">1:1</option>
      <option value="3-2">3:2</option>
      <option value="4-3">4:3</option>
    </select>
  </div>
  )
}

 const PreviewContainer = ({imageWidth, imageAspectRatio, containerAspectRatio}) => {
	 const imageHeight = imageWidth*getMultiplier(imageAspectRatio);
  return (
      <div class="image-container">
        <img class="image" src={`https://source.unsplash.com/4w8-xhdcZoU/${imageWidth}x${imageHeight}`} alt="deer"/>
      </div>
  )
}
	
	const ImageWidth = ({imageWidth, onChange}) => {
		return (
			<div class="image-width-container">
				<label htmlFor="image-width">Image Width</label>
					<input id="image-width" class="input-field" type="number" value={imageWidth} onChange={onChange} />
			</div>
		)
	}
	
	const ContainerAspectRatio = ({containerAspectRatio, onChange}) => {
		return (
			<div class="container-aspect-ratio">
				<label htmlFor="container-aspect-ratio">Container Aspect ratio</label>
				<select id="container-aspect-ratio" class="select-field" value={containerAspectRatio} onChange={onChange}>
					 <option value="16-9">16:9</option>
      <option value="3-4">3:4</option>
      <option value="1-1">1:1</option>
      <option value="3-2">3:2</option>
      <option value="4-3">4:3</option>
				</select>
			</div>
		)
	}

class App extends React.Component {
  constructor(props) {
    super(props)
				this.preview = React.createRef();
    this.state = {
      objectFitValue: "none",
      imageAspectRatio: "3-4",
					 imageWidth: "400",
					 containerAspectRatio: "16-9"
    }
  }
  objectFitChange (e) {
				this.setState({objectFitValue: e.target.value })
				let root = document.documentElement;
				root.style.setProperty('--objectFit', e.target.value);
  }
  imageAspectRatioChange(e) {
    this.setState({imageAspectRatio: e.target.value })
  }
	
	 imageWidthChange(e) {
			this.setState({imageWidth: e.target.value })
		}
	containerAspectRatioChange(e) {
		 this.setState({containerAspectRatio: e.target.value })
		 		let root = document.documentElement;
		const containerWidthInPixel =    		getComputedStyle(root).getPropertyValue('--containerWidth');
		 const containerWidth = containerWidthInPixel.split('px')[0]
			root.style.setProperty('--containerHeight', `${containerWidth*getMultiplier(e.target.value)}px`);
		}
  
render() {
	return (
 	<div class="wrapper">
			<h1 class="title">Visualize object-fit with Aspect ratios</h1>
			<p class="description">Set the container aspect ratio which is a black box. Set the image aspect ratio and the image width, height of the image will be calculated based on the width and aspect ratio of the image.Play around with object-fit property how it behaves in different container and image aspect ratios. Container width for screen size below 500px is set be 100% of the width and above all screen sizes it is set to 500px.Thanks <a href="https://unsplash.com/@thkelley">Thomas Kelley</a> for the image which I used for this demo.</p>
			<form class="form-container">
				<ContainerAspectRatio 
					containerAspectRatio=	{this.state.containerAspectRatio} 
					onChange={(e) => this.containerAspectRatioChange(e) } />
				<ImageWidth imageWidth={this.state.imageWidth} 
			           onChange={(e) => this.imageWidthChange(e)} />
  		<ImageAspectRatio onChange={(e) => this.imageAspectRatioChange(e) } 
																			imageAspectRatio={this.state.imageAspectRatio} />
				<ObjectFit onChange={(e) => this.objectFitChange(e)} 
			          value={this.state.objectFitValue} />
		</form>
  <PreviewContainer 
			ref={this.preview}
			previewAspectRatio={this.state.containerAspectRatio} 
			imageWidth={this.state.imageWidth} 
			imageAspectRatio={this.state.imageAspectRatio}
			containerAspectRatio={this.state.containerAspectRatio}/>
 </div>
)
}
}

ReactDOM.render(<App />, document.getElementById("app"))
              
            
!
999px

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