How to scroll in Javascript?

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I am at the beginning of the studies on JS, however, I am with a project, and I had the idea to make a bar Progress, however, this effect of the bar Progress will only happen, when the scroll arrives in the div of the Progress bar.

This function has been removed from the W3schools

    function move() {
      var elem = document.getElementById("myBar");  
      var porcentagem = document.querySelector("span");
      var width = 1;
      var id = setInterval(frame, 10);
      function frame() {
        if (width >= 100) {
          clearInterval(id);
        } else {
          width++;
          porcentagem.textContent =  width + '%';
          elem.style.width = width + '%'; 
        }
      }
    }
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.w3-text-cyan{color:#00bcd4!important}
.w3-text-blue-grey,.w3-text-blue-gray{color:#607d8b!important}
.w3-text-light-green{color:#8bc34a!important}
.w3-text-indigo{color:#3f51b5!important}
.w3-text-khaki{color:#b4aa50!important}
.w3-text-lime{color:#cddc39!important}
.w3-text-orange{color:#ff9800!important}
.w3-text-deep-orange{color:#ff5722!important}
.w3-text-pink{color:#e91e63!important}
.w3-text-purple{color:#9c27b0!important}
.w3-text-deep-purple{color:#673ab7!important}
.w3-text-sand{color:#fdf5e6!important}
.w3-text-teal{color:#009688!important}
.w3-text-light-grey,.w3-hover-text-light-grey:hover,.w3-text-light-gray,.w3-hover-text-light-gray:hover{color:#f1f1f1!important}
.w3-text-dark-grey,.w3-hover-text-dark-grey:hover,.w3-text-dark-gray,.w3-hover-text-dark-gray:hover{color:#3a3a3a!important}
.w3-border-red,.w3-hover-border-red:hover{border-color:#f44336!important}
.w3-border-green,.w3-hover-border-green:hover{border-color:#4CAF50!important}
.w3-border-blue,.w3-hover-border-blue:hover{border-color:#2196F3!important}
.w3-border-yellow,.w3-hover-border-yellow:hover{border-color:#ffeb3b!important}
.w3-border-white,.w3-hover-border-white:hover{border-color:#fff!important}
.w3-border-black,.w3-hover-border-black:hover{border-color:#000!important}
.w3-border-grey,.w3-hover-border-grey:hover,.w3-border-gray,.w3-hover-border-gray:hover{border-color:#bbb!important}
<div class="w3-container">
  <h2>Dynamic Progress Bar</h2>	
  <div class="w3-light-grey">
    <div id="myBar" class="w3-green" style="height:24px;width:0">       <span></span>
    </div>
  </div>
  <br>
  <button class="w3-button w3-green" onclick="move()">
    Click Me
  </button> 
</div>

In the case of the above example, the effect happens by clicking on the button, I would like to make the effect happen when the scroll arrives in the div that will effect the Progress bar.

I still don’t know what resources to use to achieve this effect, someone could help me?

2 answers

3


You can check if the scroll was to the desired element. Function credits isScrolledIntoView comes of that answer.

var wasExecuted = false;

function move() {
  var elem = document.getElementById("myBar");
  var porcentagem = document.querySelector("span");
  var width = 1;
  var id = setInterval(frame, 10);

  function frame() {
    if (width >= 100) {
      clearInterval(id);
    } else {
      width++;
      porcentagem.textContent = width + '%';
      elem.style.width = width + '%';
    }
  }
}

window.onscroll = isScrolledIntoView;

function isScrolledIntoView() {
  var elemTop = document.getElementById('myBar').getBoundingClientRect().top;
  var elemBottom = document.getElementById('myBar').getBoundingClientRect().bottom;

  var isVisible = (elemTop >= 0) && (elemBottom <= window.innerHeight);
  if (isVisible && !wasExecuted) {
    move();
    wasExecuted = true;
  }
}
#myBar {
  margin-top: 500px;
}
<div class="w3-container">
  <h2>Dynamic Progress Bar</h2>
  <div class="w3-light-grey">
    <div id="myBar" class="w3-green" style="height:24px;width:0"><span></span></div>
  </div>
  <br>

  <button class="w3-button w3-green" onclick="move()">Click Me</button>
</div>

  • is almost as I imagine, in place of the id test, would be the id myBar, then when it arrived at the bar it would load up to 100%, but this code performs the function of loading the 100% to each scroll I give, the idea is to run only once. :/

  • It is possible to use a control variable @Nicolasguilhermematheus. I edited the answer

  • Thank you Lucas, that’s exactly what I’m looking for, thank you very much.

0

You take the screen size, and according to the scroll the progress bar walks:

var body = document.body,
    html = document.documentElement;

var height = body.scrollHeight - html.clientHeight;
var valor = 0;

window.onscroll = move;

function move() {
  var doc = document.documentElement;
  var tempScrollTop = (window.pageYOffset || doc.scrollTop)  - (doc.clientTop || 0);
  var elem = document.getElementById("myBar");
  valor = (tempScrollTop * 100) / height
  elem.style.width = valor + '%';
}

Upshot: https://jsfiddle.net/Lm7vs7sb/1/

  • Thanks for the reply Wictor Keys, but the idea would be when the scroll arrived in the element Progress bar it would load its 100%, and not load its 100% based on the screen scroll size.

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