javascript - 如果未进行选择，则显示预定义值 - Javascript

Question

我有这个 JavaScript:

$(function() {

  $("#generate").click(function() {
  $("#id").val(generateID($("#age").val()));
    var increaseBy = increaseBase(generateSOCS());

    $("#numbersoc1").val(increaseBy(0));
    $("#numbersoc2").val(increaseBy(1));
    $("#numbersoc3").val(increaseBy(2));
    $("#numbersoc4").val(increaseBy(3));
  });

  $.getJSON("age.json", function(json) {

        $("#age").empty();
        $("#age").append($('<option>').text("Select age"));

        $.each(json, function(i, obj){
            $("#age").append($('<option>').text(obj.age).attr('value', obj.permanent));
        });
    });
});

function increaseBase(base) {
  return function(value) {
    return "SOCS" + (base + value).toString(16).toUpperCase()
  }
}

function generateSOCS() {
  return random(10, 16777215);
}

function generateID(permanent) {
    if(permanent == "Select age")
        return "Please select your age first!";
        var add = 5
    return (permanent + random(1,100) + random(100,50000) + ++add);
}

function random(min, max) {
  min = Math.ceil(min);
  max = Math.floor(max);
  return Math.floor(Math.random() * (max - min + 1)) + min;
}

还有这个 html:

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src='script.js'></script>
<h1>Number Generator</h1>

<div>
 <select name="age" id="age"></select><br/>

  <input id="generate" type=button value="Generate" /><br/><br/> 
  <br/>
  Identifier<br/>
   <input id="id" placeholder="Identification Number" /><br/><br/>
  Number<br/>
  <input id="numbersoc1" placeholder="Number Soc. S1." /><br/>
  <input id="numbersoc2" placeholder="Number Soc. S2." /><br/>
  <input id="numbersoc3" placeholder="Number Soc. S3." /><br/>
  <input id="numbersoc4" placeholder="Number Soc. S4." /><br/>
</div>

还有这个 json:

[
    { "age": "18", "permanent": "AA" },
    { "age": "19", "permanent": "BB" },
    { "age": "20", "permanent": "CC" }
]

当我点击“生成”按钮而不在下拉菜单中选择年龄时，“标识符”框将显示以下内容:“请先选择您的年龄!”这是正常的并且是预期的，但是我想对 4 个数字框做同样的事情。如有帮助，我们将不胜感激。

另外，代码可以提高效率吗？我的意思是更短。如果是的话怎么办？

提前谢谢您。

Answer 1

您应该首先检查#age中所选值的值。
这可以通过一个简单的 if else 语句来实现。

$("#generate").click(function() {
  if ($('#age').val() !== '<your default value>') {
    //your code for setting the values of the #numbersoc* inputs
  } else {
    //code that notifies the user about needing to select an age.
  }
});

请注意，对于此示例，您的年龄选择标记中需要有一个默认值作为选项。
这可以通过使用以下选项标签来实现。

<option selected="true" disabled="disabled">Select your age</option>  

编辑
将解决方案添加到OP的代码中。

$(function() {
  $("#generate").click(function() {
  //checks if the value of #id is an empty string
    if ($("#id").val(generateID($("#age").val())).val() == '') {
    //alerts the user that they should enter an age
    //feel free to make something nice here
      alert('Please insert age first');
    } else {
    var increaseBy = increaseBase(generateSOCS());

    $("#numbersoc1").val(increaseBy(0));
    $("#numbersoc2").val(increaseBy(1));
    $("#numbersoc3").val(increaseBy(2));
    $("#numbersoc4").val(increaseBy(3));
  }
});

  //uncomment this when using the json
  /*$.getJSON("age.json", function(json) {

    $("#age").empty();
    $("#age").append($('<option>').text('Select age').attr('value', 'Select age')
    .attr('selected', true).prop('disabled','disabled'));

    $.each(json, function(i, obj) {
      $("#age").append($('<option>').text(obj.age).attr('value', obj.permanent));
    });
  });*/
});

function increaseBase(base) {
  return function(value) {
    return "SOCS" + (base + value).toString(16).toUpperCase()
  }
}

function generateSOCS() {
  return random(10, 16777215);
}

function generateID(permanent) {
// simple check for default, empty or null value
  if ($('#age').val() == 'Select age' || $('#age').val() == '' || $('#age').val() == null) {
    return;
  }
  var add = 5
  return (permanent + random(1, 100) + random(100, 50000) + ++add);
}

function random(min, max) {
  min = Math.ceil(min);
  max = Math.floor(max);
  return Math.floor(Math.random() * (max - min + 1)) + min;
}

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

<h1>Number Generator</h1>

<div>
  <select name="age" id="age">
  <!-- the options will be auto generated -->
    <option selected="true" disabled="disabled">Select age</option>
    <option>1</option>
    <option>2</option>
    <option>3</option>
  </select>
  <br/>

  <input id="generate" type=button value="Generate" />
  <br/>
  <br/>
  <br/> Identifier
  <br/>
  <input id="id" placeholder="Identification Number" />
  <br/>
  <br/> Number
  <br/>
  <input id="numbersoc1" placeholder="Number Soc. S1." />
  <br/>
  <input id="numbersoc2" placeholder="Number Soc. S2." />
  <br/>
  <input id="numbersoc3" placeholder="Number Soc. S3." />
  <br/>
  <input id="numbersoc4" placeholder="Number Soc. S4." />
  <br/>
</div>