键盘上的Jquery

Question

我正在寻找一个函数，当某个字符键(g)按在邮政编码的第一个位置时发出警报，然后如果邮政编码开头有一个字母G，则禁用submit按钮。这个是可能的吗？

我目前要检测邮政编码字段上的密钥的代码是：

​

$(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

没有额外库的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>

​

Answer 2

您可以使用this.value[0]获取输入的第一个字符。然后测试它是否是允许的字符之一。

​

$("#input").on("keyup", function() {
  if (this.value != '') {
    var firstchar = this.value[0].toUpperCase();
    if (firstchar != 'A' && firstchar != 'G') {
      alert('not a valid postal code');
      $("#submitID").prop("disabled", true);
    } else {
      $("#submitID").prop("disabled", false);
    }
  }
});

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

​

Answer 3

看看这把小提琴http://jsfiddle.net/oyc2L9sy/12/

html：

<input id="test" type="text" />

javascript：

$(document).ready(function() {
    $("#test").on("keypress", function(e) {  
        if ((e.keyCode == '65') ||
            (e.keyCode == '71')) { 
            alert('not a valid postal code');
            return false;
        }
    });  
});