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HTML

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HTML preprocessors can make writing HTML more powerful or convenient. For instance, Markdown is designed to be easier to write and read for text documents and you could write a loop in Pug.

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About the <head>

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CSS

About CSS Preprocessors

CSS preprocessors help make authoring CSS easier. All of them offer things like variables and mixins to provide convenient abstractions.

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CSS Base

About CSS Base

It's a common practice to apply CSS to a page that styles elements such that they are consistent across all browsers. We offer two of the most popular choices: normalize.css and a reset. Or, choose Neither and nothing will be applied.

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About Vendor Prefixing

To get the best cross-browser support, it is a common practice to apply vendor prefixes to CSS properties and values that require them to work. For instance -webkit- or -moz-.

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JavaScript

About JavaScript Preprocessors

JavaScript preprocessors can help make authoring JavaScript easier and more convenient.

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Babel includes JSX processing.

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Packages

Add Packages

Search for and use JavaScript packages from npm here. By selecting a package, an import statement will be added to the top of the JavaScript editor for this package.

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Using packages here is powered by esm.sh, which makes packages from npm not only available on a CDN, but prepares them for native JavaScript ESM usage.

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HTML 

              
                <svg xmlns="http://www.w3.org/2000/svg" 
     xmlns:xlink="http://www.w3.org/1999/xlink" 
		 viewBox="0 0 1200 300"
     xml:space="preserve">
  <path class="path" d="M1130,233.5c0,0-217.7,159.8-294.4,0S433.7,331,357,201.2C264,49.3,188.6,95.5,158.1,114.9s-82.5,84.7,0,206.1"/>
</svg>

<div class="buttons-block">
  <button class='left'>Animate from left</button>
  <button class='right'>Animate from right</button>
</div>
!

CSS 

              
                body {
  background-color: rgba(100,100,100,.3); 
  display: flex;
  flex-direction: column;
  justify-content: space-around;
  align-content: center;
  height: 90vh;
}

svg {
  width: 100%;
  height: 400px;
}

.path {
  fill: none;
	stroke: red;
	stroke-width: 4;
  stroke-linecap: round;
  stroke-opacity: 0;
  transition: stroke-opacity .5s ease-in;
}
.buttons-block {
  display: flex;
  flex-direction: row;
  justify-content: space-around;
  button {
    padding: 20px;
    border: none;
    outline: none;
    text-transform: uppercase;
    background-color: lightgreen;
    font-family: sans-serif;
    font-size: 20px;
    box-shadow: inset 0px -20px 39px -18px rgba(0,0,0,0.2);
    transition: all .3s ease-in-out;
    &:hover {
      box-shadow: inset 0px 20px 39px -18px rgba(0,0,0,0.2);
    }
  }
}
!

JS 

              
                var path = document.getElementsByClassName('path').item(0),
    leftBtn = document.getElementsByClassName('left').item(0),
    rightBtn = document.getElementsByClassName('right').item(0),
    clickFlag = false;

var dashDrawInterval;

// Starting and pausing animation

// From right
rightBtn.addEventListener("click", function (){
  clickFlag = !clickFlag;
  clickFlag ? animateDashedPath(path, 10, 3000, 'right') : clearInterval(dashDrawInterval);
})

// From left
leftBtn.addEventListener("click", function() {
  clickFlag = !clickFlag;
  clickFlag ? animateDashedPath(path, 10, 3000, 'left') : clearInterval(dashDrawInterval);
})


// Animates the given path element with given dash length, animation duration and direction 
function animateDashedPath (path, dashLength, animationDuration, animationDirection) {
  
  var pathLength = path.getTotalLength(),
      numberOfSteps = Math.round(pathLength / (dashLength*2) + 1),
      stepDuration = animationDuration / numberOfSteps,
      doublePath = path.getTotalLength()*2;

  // Build the dash array so we don't have to do it manually
  var dashArray = [];
  for (var i = numberOfSteps; i > 0; i--) {
    dashArray.push(dashLength);
    dashArray.push(dashLength);
  }
  dashArray.push(pathLength);

  // Animation start conditions
  path.setAttribute("stroke-dasharray", dashArray.join(" "));
  path.setAttribute("stroke-dashoffset", -pathLength);
   
  // Animating dash until it is full 
  
  // From right to left
  function dashAnimateRight () {
    path.style.strokeOpacity = 1;
    pathLength += dashLength*2;
    path.setAttribute("stroke-dashoffset", -pathLength);
    if (pathLength > doublePath ) {
      clearInterval(dashDrawInterval);
    }
  }  
  
  
  // From left to right
  function  dashAnimateLeft() {
    path.style.strokeOpacity = 1;
    pathLength -= dashLength*2;
    path.setAttribute("stroke-dashoffset", -pathLength);
    if (pathLength <= 0) {
        clearInterval(dashDrawInterval);
    }
  }
  
  if (animationDirection === 'right' ) {
    dashDrawInterval = setInterval(dashAnimateRight, stepDuration);  
  }
  
  if (animationDirection === 'left' ) {
    dashDrawInterval = setInterval(dashAnimateLeft, stepDuration);  
  }
}
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999px

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