JS脚本没有按顺序下载和评估

使用回调函数或Promise来保证脚本顺序下载和评估。

示例代码：使用回调函数

function loadScript(url, callback) {
  var script = document.createElement('script');
  script.type = 'text/javascript';
  script.src = url;
  script.onload = function() {
    if (callback) {
      callback();
    }
  };
  document.head.appendChild(script);
}

loadScript('script1.js', function() {
  loadScript('script2.js', function() {
    loadScript('script3.js', function() {
      //all scripts have been loaded and evaluated
    });
  });
});

示例代码：使用Promise

function loadScript(url) {
  return new Promise(function(resolve, reject) {
    var script = document.createElement('script');
    script.type = 'text/javascript';
    script.src = url;
    script.onload = function() {
      resolve();
    };
    script.onerror = function() {
      reject();
    };
    document.head.appendChild(script);
  });
}

loadScript('script1.js')
  .then(function() {
    return loadScript('script2.js');
  })
  .then(function() {
    return loadScript('script3.js');
  })
  .then(function() {
    //all scripts have been loaded and evaluated
  })
  .catch(function() {
    //handle errors here
  });