如何使谷歌图表动画仅在滚动时才开始？

Question

您好，我想知道如何使 google 图表动画仅在滚动和出现时才开始。

  <script type="text/javascript" src="https://www.gstatic.com/charts/loader.js"></script>
  <div id="chart_div"></div>


google.charts.load('current', {packages: ['corechart', 'bar']});
google.charts.setOnLoadCallback(drawMultSeries);

function drawMultSeries() {
  var data = google.visualization.arrayToDataTable([
    ['City', '2010 Population', '2000 Population'],
    ['New York City, NY', 8175000, 8008000],
    ['Los Angeles, CA', 3792000, 3694000],
    ['Chicago, IL', 2695000, 2896000],
    ['Houston, TX', 2099000, 1953000],
    ['Philadelphia, PA', 1526000, 1517000]
  ]);

 var options = {  
              animation: {
            duration: 2000,
            startup: true //This is the new option
        },
           };  

  var chart = new google.visualization.BarChart(document.getElementById('chart_div'));
  chart.draw(data, options);
}

Answer 1

您可以在滚动时添加侦听器，并且仅在条件下加载谷歌图表（“当用户滚动通过#chart_div”）：

let alreadyLoaded = false ;     
window.addEventListener('scroll', function(){
if (alreadyLoaded === false){

        var element = document.querySelector('#chart_div');
        var position = element.getBoundingClientRect();
    
    
        if(position.top >= 0 && position.bottom <= window.innerHeight) {

    
        // checking for partial visibility
        if(position.top < window.innerHeight && position.bottom >= 0) {
    alreadyLoaded = true;  
       google.charts.load('current', {packages: ['corechart', 'bar']});
    google.charts.setOnLoadCallback(drawMultSeries);
    
    function drawMultSeries() {
      var data = google.visualization.arrayToDataTable([
        ['City', '2010 Population', '2000 Population'],
        ['New York City, NY', 8175000, 8008000],
        ['Los Angeles, CA', 3792000, 3694000],
        ['Chicago, IL', 2695000, 2896000],
        ['Houston, TX', 2099000, 1953000],
        ['Philadelphia, PA', 1526000, 1517000]
      ]);
    
     var options = {  
                  animation: {
                duration: 2000,
                startup: true //This is the new option
            },
               };  
    
      var chart = new google.visualization.BarChart(document.getElementById('chart_div'));
      chart.draw(data, options);
    }
      }
}
     });