javascript - 按键上的 Jquery

Question

我正在寻找一个功能，当在邮政编码的第一个位置按下某个字符键(g)时发出警报，然后如果邮政编码以字母 G 开头则禁用提交按钮。 这可能吗？

我当前检测邮政编码字段上的键的代码是这样的:

$(document).ready(function() {
  var someTextInputField = "#postal-code";
  
  $(someTextInputField).on("keyup", function() {
    alert('not a valid postal code');
  });
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

<input id="postal-code" />

Answer 1

无需额外库的 JavaScript

document.addEventListener("input", function(e) {
  if (e.target.id === "postal-code") {
    var disable = /^g/i.test(e.target.value),
      submit = document.getElementById("submit");
    
    if (disable && !submit.disabled) {
      alert("You cannot start a postal code with a G");
    }
    
    submit.disabled = disable;
  }
});

<input placeholder="Address" />
<input id="postal-code" placeholder="Postal Code" />
<button id="submit">Submit</button>

jQuery

$(document).on("input", "#postal-code", function (e) {
  var disable = /^g/i.test(this.value),
      $submit = $("#submit");
    
    if (disable && !$submit.prop("disabled")) {
      alert("You cannot start a postal code with a G");
    }
    
    $submit.prop("disabled", disable);
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

<input placeholder="Address" />
<input id="postal-code" placeholder="Postal Code" />
<button id="submit">Submit</button>