jQuery - 检测隐藏输入字段的值变化

Question

我有一个隐藏的文本字段，其值通过 AJAX 响应更新。

<input type="hidden" value="" name="userid" id="useid" />

当这个值改变时，我想触发一个 AJAX 请求。谁能建议如何检测变化？

我有以下代码，但不知道如何查找值：

$('#userid').change( function() {  
    alert('Change!'); 
}) 

Answer 1

所以这已经很晚了，但我发现了一个答案，以防万一它对遇到此线程的任何人有用。

对隐藏元素的值更改不会自动触发 .change() 事件。因此，无论您在哪里设置该值，您还必须告诉 jQuery 触发它。

function setUserID(myValue) {
     $('#userid').val(myValue)
                 .trigger('change');
}

既然如此，

$('#userid').change(function(){
      //fire your ajax call  
})

应该按预期工作。

Answer 2

由于隐藏输入不会在更改时触发“更改”事件，因此我使用 MutationObserver 来触发此事件。

（有时隐藏的输入值更改是由您无法修改的其他脚本完成的）

这在 IE10 及以下版本中不起作用

MutationObserver = window.MutationObserver || window.WebKitMutationObserver;

var trackChange = function(element) {
  var observer = new MutationObserver(function(mutations, observer) {
    if(mutations[0].attributeName == "value") {
        $(element).trigger("change");
    }
  });
  observer.observe(element, {
    attributes: true
  });
}

// Just pass an element to the function to start tracking
trackChange( $("input[name=foo]")[0] );

Answer 3

你可以简单地使用下面的函数，你也可以改变类型元素。

 $("input[type=hidden]").bind("change", function() {
       alert($(this).val()); 
 });

对隐藏元素的值更改不会自动触发 .change() 事件。所以，无论你在哪里设置这个值，你也必须告诉 jQuery 来触发它。

HTML

 <div id="message"></div>
<input type="hidden" id="testChange" value="0"  />    

JAVASCRIPT

var $message = $('#message');
var $testChange = $('#testChange');
var i = 1;

function updateChange() {
    $message.html($message.html() + '<p>Changed to ' + $testChange.val() + '</p>');
}

$testChange.on('change', updateChange);

setInterval(function() {
    $testChange.val(++i).trigger('change');; 
    console.log("value changed" +$testChange.val());
}, 3000);

updateChange();

应该按预期工作。

http://jsfiddle.net/7CM6k/3/

Answer 4

$('#userid').change(function(){
  //fire your ajax call  
});

$('#userid').val(10).change();

Answer 5

可以使用Object.defineProperty() 来重新定义输入元素的“值”属性并在其更改期间执行任何操作。

Object.defineProperty() 允许我们为属性定义 getter 和 setter，从而控制它。

replaceWithWrapper($("#hid1")[0], "value", function(obj, property, value) { 
  console.log("new value:", value)
});

function replaceWithWrapper(obj, property, callback) {
  Object.defineProperty(obj, property, new function() {
    var _value = obj[property];
    return {
      set: function(value) {
        _value = value;
        callback(obj, property, value)
      },
      get: function() {
        return _value;
      }
    }
  });
}

$("#hid1").val(4);

https://jsfiddle.net/bvvmhvfk/

Answer 6

在Viktar's answer 的基础上，您可以在给定的隐藏输入元素上调用一次，以确保在输入元素的值发生更改时触发后续更改事件：

/**
 * Modifies the provided hidden input so value changes to trigger events.
 *
 * After this method is called, any changes to the 'value' property of the
 * specified input will trigger a 'change' event, just like would happen
 * if the input was a text field.
 *
 * As explained in the following SO post, hidden inputs don't normally
 * trigger on-change events because the 'blur' event is responsible for
 * triggering a change event, and hidden inputs aren't focusable by virtue
 * of being hidden elements:
 * https://stackoverflow.com/a/17695525/4342230
 *
 * @param {HTMLInputElement} inputElement
 *   The DOM element for the hidden input element.
 */
function setupHiddenInputChangeListener(inputElement) {
  const propertyName = 'value';

  const {get: originalGetter, set: originalSetter} =
    findPropertyDescriptor(inputElement, propertyName);

  // We wrap this in a function factory to bind the getter and setter values
  // so later callbacks refer to the correct object, in case we use this
  // method on more than one hidden input element.
  const newPropertyDescriptor = ((_originalGetter, _originalSetter) => {
    return {
      set: function(value) {
        const currentValue = originalGetter.call(inputElement);

        // Delegate the call to the original property setter
        _originalSetter.call(inputElement, value);

        // Only fire change if the value actually changed.
        if (currentValue !== value) {
          inputElement.dispatchEvent(new Event('change'));
        }
      },

      get: function() {
        // Delegate the call to the original property getter
        return _originalGetter.call(inputElement);
      }
    }
  })(originalGetter, originalSetter);

  Object.defineProperty(inputElement, propertyName, newPropertyDescriptor);
};

/**
 * Search the inheritance tree of an object for a property descriptor.
 *
 * The property descriptor defined nearest in the inheritance hierarchy to
 * the class of the given object is returned first.
 *
 * Credit for this approach:
 * https://stackoverflow.com/a/38802602/4342230
 *
 * @param {Object} object
 * @param {String} propertyName
 *   The name of the property for which a descriptor is desired.
 *
 * @returns {PropertyDescriptor, null}
 */
function findPropertyDescriptor(object, propertyName) {
  if (object === null) {
    return null;
  }

  if (object.hasOwnProperty(propertyName)) {
    return Object.getOwnPropertyDescriptor(object, propertyName);
  }
  else {
    const parentClass = Object.getPrototypeOf(object);

    return findPropertyDescriptor(parentClass, propertyName);
  }
}

在准备好的文档上调用它，如下所示：

$(document).ready(function() {
  setupHiddenInputChangeListener($('myinput')[0]);
});

Answer 7

此示例在每次隐藏草稿字段更改其值时返回草稿字段值（chrome 浏览器）：

var h = document.querySelectorAll('input[type="hidden"][name="draft"]')[0];
//or jquery.....
//var h = $('input[type="hidden"][name="draft"]')[0];

observeDOM(h, 'n', function(draftValue){ 
  console.log('dom changed draftValue:'+draftValue);
});


var observeDOM = (function(){
var MutationObserver = window.MutationObserver || 
window.WebKitMutationObserver;

  return function(obj, thistime, callback){
    if(typeof obj === 'undefined'){
      console.log('obj is undefined');
      return;
    }

    if( MutationObserver ){

        // define a new observer
        var obs = new MutationObserver(function(mutations, observer){

            if( mutations[0].addedNodes.length || mutations[0].removedNodes.length ){

               callback('pass other observations back...');

            }else if(mutations[0].attributeName == "value" ){

               // use callback to pass back value of hidden form field                            
               callback( obj.value );

            }

        });

        // have the observer observe obj for changes in children
        // note 'attributes:true' else we can't read the input attribute value
        obs.observe( obj, { childList:true, subtree:true, attributes:true  });

       }
  };
})();

Answer 8

虽然这个帖子有 3 年的历史，但这是我的解决方案：

$(function ()
{
    keep_fields_uptodate();
});

function keep_fields_uptodate()
{
    // Keep all fields up to date!
    var $inputDate = $("input[type='date']");
    $inputDate.blur(function(event)
    {
        $("input").trigger("change");
    });
}