Web组件接收超长的字符串时会被截断

Web({ src: $rawfile("index.html"), controller: this.controller }) 
  .onAlert((event) => { 
    let result: string | undefined = event?.message 
    let str1 = result?.substring(0, 10) 
    let str2 = result?.substring(result.length - 10, result.length) 
    console.log('zqf' + str1) 
    console.log('zqf' + str2) 
    return true 
  }) 
 
html代码如下： 
<button onclick="myFunction()">Click here</button> 
  <script> 
  function downloadTextFile(filename, text) { 
    // 创建一个Blob实例，类型为纯文本 
    var blob = new Blob([text], { type: 'text/plain' }); 
 
    // 创建一个指向Blob的URL 
    var url = URL.createObjectURL(blob); 
 
    // 创建一个a标签 
    var a = document.createElement('a'); 
    a.href = url; 
    a.download = filename; 
 
    // 模拟a标签点击，触发下载 
    document.body.appendChild(a); 
    a.click(); 
 
    // 清理临时DOM和对象URL 
    document.body.removeChild(a); 
    URL.revokeObjectURL(url); 
  } 
let str = '开头'; 
for (let i = 0; i < 1000 * 1000; i++) { 
  str += '这是要保存到本地的文本内容' 
} 
str += '结尾' 
function myFunction() { 
  let str1 = str.substring(0, 10) 
  let str2 = str.substring(str.length - 10, str.length) 
  console.log(str1) 
  console.log(str2) 
  alert(str) 
}