jQuery - 检测隐藏输入字段的值更改

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,我想发出一个AJAX请求.任何人都可以建议如何检测变化？

我有以下代码,但不知道如何查找值:

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

Answer 1

所以这是迟到的,但我发现了一个答案,以防它对遇到这个帖子的人有用.

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

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

一旦发生这种情况,

$('#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来触发此操作.

(有时隐藏的输入值更改由您无法修改的其他脚本完成)

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

您可以简单地使用以下功能,您也可以更改类型元素.

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

隐藏元素的值更改不会自动触发.change()事件.因此,无论您在何处设置该值,您还必须告诉jQuery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

基于Viktar 的回答，这里有一个实现，您可以在给定的隐藏输入元素上调用一次，以确保每当输入元素的值发生变化时都会触发后续的更改事件：

/**
 * 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:
 * /sf/answers/1238686781/
 *
 * @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:
 * /sf/answers/2716182171/
 *
 * @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);
  }
}

在文档准备好时调用它，如下所示：

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