JavaScript　パスワード生成

配列からランダムな引数をとるには、Math.floor(Math.random() * xxx.length)のように書きます。

<!DOCTYPE html>
<html lang="ja">
  <head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Password Generator</title>
    <link rel="stylesheet" href="styles.css">
    <style>
      body {
        background: #e0e0e0;
        text-align: center;
        font-family: 'Courier New', sans-serif;
      }
      .container {
        width: 320px;
        margin: 30px auto;
      }
      input[type="text"]{
        width: 300px;
        padding: 7px;
        border-radius: 3px;
        font-size: 24px;
        font-family: 'Courier New', sans-serif;
        text-align: center;
      }
      #btn {
        color: #fff;
        background: #00aaff;
        padding: 7px;
        border-radius: 5px;
        box-shadow: 0 4px 0 #0088cc;
        cursor: pointer;
      }
      #btn:hover {
        opacity: 0.8;
      }
      fieldset {
        margin-top: 40px;
        border: 1px dashed #aaa;
        border-radius: 5px;
        text-align: left;
      }
      legend {
        font-weight: bold;
        padding: 0 10px;
      }
      fieldset p {
        text-align: center;
      }
    </style>
  </head>
  <body>
      <div class="container">
        <p><input type="text" id="result"></p>
        <p><div id="btn">Generate Password</div></p>
        <fieldset>
          <legend>Options</legend>
          <p>Length(<span id="label">8</span>): <input type="range" id="slider" value="8" min="4" max="20"</p>
          <p>
            Numbers?: <input type="checkbox" id="numbers">
            Symbols?: <input type="checkbox" id="symbols">
          </p>
        </fieldset>
        </div>
      <script>

          (function(){
              'use strict'

              var slider = document.getElementById('slider');
              var label = document.getElementById('label');
              var btn = document.getElementById('btn');
              var result = document.getElementById('result');
              var numbers = document.getElementById('numbers');
              var symbols = document.getElementById('symbols');

              function getPassword(){
                var seed_letters = 'abcdefghijklmnopqrstuvwxyz';
                var seed_numbers = '0123456789';
                var seed_symbols = '!#$%&()';
                var seed;
                var len = slider.value;
                var pwd = '';

                seed = seed_letters + seed_letters.toUpperCase();
                if (numbers.checked === true){
                  seed += seed_numbers;
                }
                 if (symbols.checked === true){
                  seed += seed_symbols;
                }

               // for (var i = 0; i < len; i++){
               //   pwd += seed&#91;Math.floor(Math.random() * seed.length)&#93;;
               // }
                while(len--){
                  pwd += seed&#91;Math.floor(Math.random() * seed.length)&#93;;
                }

                result.value = pwd;
              }
              slider.addEventListener('change', function(){
                  label.innerHTML = this.value;
              });
              btn.addEventListener('click', function(){
                  getPassword();
                  // result.value = 'asdfasdf';
              });
              result.addEventListener('click', function(){
                  this.select();
              });

              getPassword();



          })();

      </script>
  </body>
</html>

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