a.html

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <h2>红包生成器</h2>
<div id="setting">
  <div><label>红包金额：<input id="amount" value=100.00></input></label></div>
  <div><label>红包数量：<input id="count" value="10"></input></label></div>
  <div><button id="generateBtn">随机生成</button></div>
</div>

<ul id="result">
</ul>
<script>
  function generate(amount, count){
  let ret = [amount];
  
  while(count > 1){
    //挑选出最大一块进行切分
    let cake = Math.max(...ret),
    
        idx = ret.indexOf(cake),
        part = 1 + Math.floor((cake / 2) * Math.random()),
        rest = cake - part;
    console.log(cake);
    
    ret.splice(idx, 1, part, rest);
    
    count--;
  }
  return ret;
}

const amountEl = document.getElementById('amount');
const countEl = document.getElementById('count');
const generateBtn = document.getElementById('generateBtn');
const resultEl = document.getElementById('result');

generateBtn.onclick = function(){
  let amount = Math.round(parseFloat(amountEl.value) * 100);
  let count = parseInt(countEl.value);
  
  let output = [];
  
  if(isNaN(amount) || isNaN(count) 
     || amount <= 0 || count <= 0){
    output.push('输入格式不正确！');
  }else if(amount < count){
    output.push('钱不够分')
  }else{
    output.push(...generate(amount, count));
    output = output.map(m => (m / 100).toFixed(2));
  }
  resultEl.innerHTML = '<li>' + 
                        output.join('</li><li>') +
                       '</li>';
}


</script>
</body>
</html>