Can jQuery check whether input content has changed

问题:

Is it possible to bind javascript (jQuery is best) event to "change" form input value somehow?

I know about .change() method, but it does not trigger until you (the cursor) leave(s) the input field. I have also considered using .keyup() method but it reacts also on arrow keys and so on.

I need just trigger an action every time the text in the input changes, even if it's only one letter change.

回答1:

There is a simple solution, which is the HTML5 input event. It's supported in current versions of all major browsers for <input type="text"> elements and there's a simple workaround for IE < 9. See the following answers for more details:

• jQuery keyboard events
• Catch only keypresses that change input?

Example (except IE < 9: see links above for workaround):

$("#your_id").on("input", function() {
    alert("Change to " + this.value);
});

回答2:

Yes, compare it to the value it was before it changed.

var previousValue = $("#elm").val();
$("#elm").keyup(function(e) {
    var currentValue = $(this).val();
    if(currentValue != previousValue) {
         previousValue = currentValue;
         alert("Value changed!");
    }
});

Another option is to only trigger your changed function on certain keys. Use e.KeyCode to figure out what key was pressed.

回答3:

function checkChange($this){
    var value = $this.val();      
    var sv=$this.data("stored");            
        if(value!=sv)
            $this.trigger("simpleChange");    
}

$(document).ready(function(){
    $(this).data("stored",$(this).val());   
        $("input").bind("keyup",function(e){  
        checkChange($(this));
    });        
    $("input").bind("simpleChange",function(e){
        alert("the value is chaneged");
    });        
});

here is the fiddle http://jsfiddle.net/Q9PqT/1/

回答4:

You can also store the initial value in a data attribute and test it with the current value.

<input type="text" name="somename" id="id_someid" value="" data-initial="your initial value" /> 

$("#id_someid").keyup(function() {
    return $(this).val() == $(this).data().initial;
});

Would return true if the initial value has not changed.

回答5:

You can employ the use of data in jQuery and catch all of the events which then tests it against it's last value (untested):

$(document).ready(function() {  
    $("#fieldId").bind("keyup keydown keypress change blur", function() {
        if ($(this).val() != jQuery.data(this, "lastvalue") {
         alert("changed");
        }
        jQuery.data(this, "lastvalue", $(this).val());
    });
});

This would work pretty good against a long list of items too. Using jQuery.data means you don't have to create a javascript variable to track the value. You could do $("#fieldId1, #fieldId2, #fieldId3, #fieldId14, etc") to track many fields.

UPDATE: Added blur to the bind list.

回答6:

I had to use this kind of code for a scanner that pasted stuff into the field

$(document).ready(function() {
  var tId,oldVal;
  $("#fieldId").focus(function() {
     oldVal = $("#fieldId").val();
     tId=setInterval(function() { 
      var newVal = $("#fieldId").val(); 
      if (oldVal!=newVal) oldVal=newVal;
      someaction() },100);
  });
  $("#fieldId").blur(function(){ clearInterval(tId)});
});

Not tested...

回答7:

I don't think there's a 'simple' solution. You'll probably need to use both the events onKeyUp and onChange so that you also catch when changes are made with the mouse. Every time your code is called you can store the value you've 'seen' on this.seenValue attached right to the field. This should make a little easier.

回答8:

You can set events on a combination of key and mouse events, and onblur as well, to be sure. In that event, store the value of the input. In the next call, compare the current value with the lastly stored value. Only do your magic if it has actually changed.

To do this in a more or less clean way:

You can associate data with a DOM element (lookup api.jquery.com/jQuery.data ) So you can write a generic set of event handlers that are assigned to all elements in the form. Each event can pass the element it was triggered by to one generic function. That one function can add the old value to the data of the element. That way, you should be able to implement this as a generic piece of code that works on your whole form and every form you'll write from now on. :) And it will probably take no more than about 20 lines of code, I guess.

An example is in this fiddle: http://jsfiddle.net/zeEwX/

回答9:

Since the user can go into the OS menu and select paste using their mouse, there is no safe event that will trigger this for you. The only way I found that always works is to have a setInterval that checks if the input value has changed:

var inp = $('#input'),
    val = saved = inp.val(),
    tid = setInterval(function() {
        val = inp.val();
        if ( saved != val ) {
            console.log('#input has changed');
            saved = val;
    },50);

You can also set this up using a jQuery special event.