<section> <form id="sampleForm"> <label> 半角英数字以外を入力してみよう <input type="text" id="input" placeholder="半角英数字で入力" pattern="^[0-9A-Za-z]+$" required> </label> <button type="submit" id="submit">送信</button> </form> </section> <script> "use strict"; var form = document.getElementById("sampleForm"), input = document.getElementById("input"), submit = document.getElementById("submit"); input.addEventListener
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