배열과 반복문 활용

 <h1><a href="index.html">WEB</a></h1>
    <input
      id="night_day"
      type="button"
      value="night"
      onclick="
    var target = document.querySelector('body');
    if(this.value === 'night'){
      target.style.backgroundColor = 'black';
      target.style.color = 'white';
      this.value = 'day';

      var alist = document.querySelectorAll('a');
      var i = 0;
      while(i < alist.length){
        alist[i].style.color = 'powderblue';
        i = i + 1;
      }
    } else {
      target.style.backgroundColor = 'white';
      target.style.color = 'black';
      this.value = 'night';

      var alist = document.querySelectorAll('a');
      var i = 0;
      while(i < alist.length){
        alist[i].style.color = 'blue';
        i = i + 1;
      }
    }
  "
    />
    <ol>
      <li><a href="1.html">HTML</a></li>
      <li><a href="2.html">CSS</a></li>
      <li><a href="3.html">JavaScript</a></li>
    </ol>
    <h2>JavaScript</h2>
    <p>
      JavaScript (/ˈdʒɑːvəˌskrɪpt/[6]), often abbreviated as JS, is a
      high-level, dynamic, weakly typed, prototype-based, multi-paradigm, and
      interpreted programming language. Alongside HTML and CSS, JavaScript is
      one of the three core technologies of World Wide Web content production.
      It is used to make webpages interactive and pr
    </p>