Develop Reference

How to know the valueChanged origin in Aurelia?

I created a custom element in Aurelia and I also have the valueChanged, however I need to do a certain action only when the value is changed outside of the custom element. Since the signature is valueChanged(newValue, oldValue), how would I know when the value gets changed from the ViewModel and not from the custom element itself? Is that doable somehow with an observer or observable?
I actually got kind of a working sample, I saw that there's also an __array_observer__ property when the value is changed from the ViewModel, and it works but it's probably not ideal. So I got this piece of code which kinda works
valueChanged(newValue, oldValue) {
if (newValue !== oldValue && newValue.__array_observer__) {
// value got changed outside of this custom element
}
}
This is probably not ideal though, or is it? Any other suggestion in knowing where the value got changed outside of the custom element?
EDIT
As much as possible, I'm looking for a solution that will still have access to the custom element. Even if I want to get triggered by an external value change call, I still need to call an internal function of the same custom element.
EDIT #2
To give a little more description of my issue, I need to know when the value got changed from the outside because this will trigger an action that will re-affect the value. Without knowing if the change was from the outside of the custom element, I fall in a recursive call with no way to stop it. What I'm looking for is similar to what used to be the caller and the callee but this was removed with ES5 and Strict Mode, however this would have been very useful.
Still looking for an answer :(

You could use a CustomBindingBehavior to intercept the updateTarget event. For instance:
export class InterceptBindingBehavior {
bind(binding, scope, interceptor) {
binding['originalUpdateTarget'] = binding['updateTarget'];
binding.updateTarget = val => {
alert('property was changed outside of the element');
//do something here
binding['originalUpdateTarget'](val);
}
}
unbind(binding, scope) {
binding.updateTarget = binding['originalUpdateTarget'];
binding['originalUpdateTarget'] = null;
}
}
Usage:
<template>
<require from="./intercept-binding-behavior"></require>
<some-element value.bind="message & intercept"></some-element>
</template>
Runnable example: https://gist.run/?id=bcd7d39ed94856caf586f224f89fd1ff
I haven't tested this in many cases and I'm not sure if it's best way.
If you want to do the opposite (intercept when the property is changed from the element instead of the VM) just replace updateTarget for updateSource.
More info about CustomBindingBehaviors http://aurelia.io/hub.html#/doc/article/aurelia/binding/latest/binding-binding-behaviors/8
Hope this helps!

As discussed in gitter, you can use a suppress flag
value: number;
suppressValueChanged: boolean;
valueChanged(){
if(this.suppressValueChanged){
this.suppressValueChanged = false;
this.logger.debug("the value has been changed from inside the element");
return;
}
this.logger.debug("the value has been changed from outside the element");
// here comes the code to run when the value is changed outside
}
internalSetValue(value: number){
this.suppressValueChanged = true;
this.value = value;
}
The reason I reset the flag in the changed method is that depending on the circumstances valueChanged can be called by Aurelia asynchronously so you cannot just do the following
this.suppressValueChanged = true;
this.value = 123;
this.suppressValueChanged = false;
Sometimes, using a task will work
this.taskQueue.queueTask(() => {
this.suppressValueChanged = true;
this.value = 123;
this.suppressValueChanged = false;
});
It really depends where exactly in Aurelia code you are changing the value. I've found that the first option gives the most consistent result.

Simulating text entry with reactJs TestUtils

I want to be able to simulate a user typing into a text box using reactjs so that I can test my validation status messages.
I have a react component which validates on keyUp
Below is a simple example of what I've tried.
nameInput.props.value = 'a';
React.addons.TestUtils.Simulate.keyUp(nameInput);
React.addons.TestUtils.findRenderedDOMComponentWithClass(component, 'has-error');
This doesn't seem to change the value of the bound textbox when I debug in the validator
React.addons.TestUtils.Simulate.keyUp(nameInput, {key: 'a'});
React.addons.TestUtils.findRenderedDOMComponentWithClass(component, 'has-error');
This doesn't either.
Could someone point me on the right track, the second is inline with the documentation I could find around simulate (http://facebook.github.io/react/docs/test-utils.html), the first makes sense to me (set the actual textbox value then fake an event)

By setting nameInput.props.value = 'a'; you are not actually updating the value in your component.
You should use React.addons.TestUtils.Simulate.change(nameInput, { target: { value: 'a' } }); or something similar to simulate modifying the actual value.

I found that this syntax works better for me:
const emailInput = component.refs.userEmailInput;
emailInput.value = 'test#gmail.com';
Simulate.change(component.refs.userEmailInput);
The second line updates the input with the text, 'test#gmail.com'. The last line triggers the change.

Avoid "ifChanged" event handler when setting checkbox via Javascript

for iCheck plugin, is there a way to avoid "ifChanged" event handler to fire up when setting the checkbox from Javascript?

Old question, but I found a better method is to check the event.target.checked property and only run your code if it returns true. iCheck fires ifChanged twice - first for the un-checked option, then secondly for the checked option. So if you only run your code if event.target.checked === true, you will get the result you are after.

You could create a variable ignoreChange and when subscribing to the event handler, checking whether that variable is true and if it is, then set it to false and stop the function. If it is not true, then you can execute your normal code.
JS code:
var ignoreChange = false;
$('input').on('ifChanged', function(event){
if (ignoreChange) {
ignoreChange = false;
return;
}
// do stuff
});
// When changing the checkbox
ignoreChange = true;
Basically, whenever you set the variable ignoreChange to true, the next event call is ignored. This is quite a hacky workaround, however necessary, as I did not find a way to solve your problem trough the iCheck library.

Trigger action on programmatic change to an input value

My objective is to observe an input value and trigger a handler when its value gets changed programmatically. I only need it for modern browsers.
I have tried many combinations using defineProperty and this is my latest iteration:
var myInput=document.getElementById("myInput");
Object.defineProperty(myInput,"value",{
get:function(){
return this.getAttribute("value");
},
set:function(val){
console.log("set");
// handle value change here
this.setAttribute("value",val);
}
});
myInput.value="new value"; // should trigger console.log and handler
This seems to do what I expect, but it feels like a hack as I am overriding the existing value property and playing with the dual status of value (attribute and property). It also breaks the change event that doesn't seem to like the modified property.
My other attempts:
a setTimeout/setInterval loop, but this is not clean either
various watch and observe polyfills, but they break for an input value property
What would be a proper way to achieve the same result?
Live demo: http://jsfiddle.net/L7Emx/4/
[Edit] To clarify: My code is watching an input element where other applications can push updates (as a result of ajax calls for example, or as a result of changes in other fields). I have no control on how the other applications push updates, I am just an observer.
[Edit 2] To clarify what I mean by "modern browser", I'd be very happy with a solution that works on IE 11 and Chrome 30.
[Update] Updated demo based on the accepted answer: http://jsfiddle.net/L7Emx/10/
The trick suggested by #mohit-jain is to add a second input for user interaction.

if the only problem with your solution is breaking of change event on value set. thn you can fire that event manually on set. (But this wont monitor set in case a user makes a change to the input via browser -- see edit bellow)
<html>
<body>
<input type='hidden' id='myInput' />
<input type='text' id='myInputVisible' />
<input type='button' value='Test' onclick='return testSet();'/>
<script>
//hidden input which your API will be changing
var myInput=document.getElementById("myInput");
//visible input for the users
var myInputVisible=document.getElementById("myInputVisible");
//property mutation for hidden input
Object.defineProperty(myInput,"value",{
get:function(){
return this.getAttribute("value");
},
set:function(val){
console.log("set");
//update value of myInputVisible on myInput set
myInputVisible.value = val;
// handle value change here
this.setAttribute("value",val);
//fire the event
if ("createEvent" in document) { // Modern browsers
var evt = document.createEvent("HTMLEvents");
evt.initEvent("change", true, false);
myInput.dispatchEvent(evt);
}
else { // IE 8 and below
var evt = document.createEventObject();
myInput.fireEvent("onchange", evt);
}
}
});
//listen for visible input changes and update hidden
myInputVisible.onchange = function(e){
myInput.value = myInputVisible.value;
};
//this is whatever custom event handler you wish to use
//it will catch both the programmatic changes (done on myInput directly)
//and user's changes (done on myInputVisible)
myInput.onchange = function(e){
console.log(myInput.value);
};
//test method to demonstrate programmatic changes
function testSet(){
myInput.value=Math.floor((Math.random()*100000)+1);
}
</script>
</body>
</html>
more on firing events manually
EDIT:
The problem with manual event firing and the mutator approach is that the value property won't change when user changes the field value from browser. the work around is to use two fields. one hidden with which we can have programmatic interaction. Another is visible with which user can interact. After this consideration approach is simple enough.
mutate value property on hidden input-field to observe the changes and fire manual onchange event. on set value change the value of visible field to give user feedback.
on visible field value change update the value of hidden for observer.

The following works everywhere I've tried it, including IE11 (even down to IE9 emulation mode).
It takes your defineProperty idea a bit further by finding the object in the input element prototype chain that defines the .value setter and modifying this setter to trigger an event (I've called it modified in the example), while still keeping the old behavior.
When you run the snippet below, you can type / paste / whatnot in the text input box, or you can click the button that appends " more" to the input element's .value. In either case, the <span>'s content is synchronously updated.
The only thing that's not handled here is an update caused by setting the attribute. You could handle that with a MutationObserver if you want, but note that there's not a one-to-one relationship between .value and the value attribute (the latter is just the default value for the former).
// make all input elements trigger an event when programmatically setting .value
monkeyPatchAllTheThings();
var input = document.querySelector("input");
var span = document.querySelector("span");
function updateSpan() {
span.textContent = input.value;
}
// handle user-initiated changes to the value
input.addEventListener("input", updateSpan);
// handle programmatic changes to the value
input.addEventListener("modified", updateSpan);
// handle initial content
updateSpan();
document.querySelector("button").addEventListener("click", function () {
input.value += " more";
});
function monkeyPatchAllTheThings() {
// create an input element
var inp = document.createElement("input");
// walk up its prototype chain until we find the object on which .value is defined
var valuePropObj = Object.getPrototypeOf(inp);
var descriptor;
while (valuePropObj && !descriptor) {
descriptor = Object.getOwnPropertyDescriptor(valuePropObj, "value");
if (!descriptor)
valuePropObj = Object.getPrototypeOf(valuePropObj);
}
if (!descriptor) {
console.log("couldn't find .value anywhere in the prototype chain :(");
} else {
console.log(".value descriptor found on", "" + valuePropObj);
}
// remember the original .value setter ...
var oldSetter = descriptor.set;
// ... and replace it with a new one that a) calls the original,
// and b) triggers a custom event
descriptor.set = function () {
oldSetter.apply(this, arguments);
// for simplicity I'm using the old IE-compatible way of creating events
var evt = document.createEvent("Event");
evt.initEvent("modified", true, true);
this.dispatchEvent(evt);
};
// re-apply the modified descriptor
Object.defineProperty(valuePropObj, "value", descriptor);
}
<input><br><br>
The input contains "<span></span>"<br><br>
<button>update input programmatically</button>

I only need it for modern browsers.
How modern would you like to go? Ecma Script 7 (6 will be made final in December) might contain Object.observe. This would allow you to create native observables. And yes, you can run it! How?
To experiment with this feature, you need to enable the Enable
Experimental JavaScript flag in Chrome Canary and restart the browser.
The flag can be found under 'about:flags’
More info: read this.
So yeah, this is highly experimental and not ready in the current set of browsers. Also, it's still not fully ready and not 100% if it's coming to ES7, and the final date for ES7 isn't even set yet. Still, I wanted to let you know for future use.

Since you are already using polyfills for watch/observe, etc, let me take the opportunity to suggest to you Angularjs.
It offers exactly this functionality in the form of it's ng-models. You can put watchers on the model's value, and when it changes, you can then call other functions.
Here is a very simple, but working solution to what you want:
http://jsfiddle.net/RedDevil/jv8pK/
Basically, make a text input and bind it to a model:
<input type="text" data-ng-model="variable">
then put a watcher on the angularjs model on this input in the controller.
$scope.$watch(function() {
return $scope.variable
}, function(newVal, oldVal) {
if(newVal !== null) {
window.alert('programmatically changed');
}
});

There is a way to do this.
There is no DOM event for this, however there is a javascript event that triggers on an object property change.
document.form1.textfield.watch("value", function(object, oldval, newval){})
^ Object watched ^ ^ ^
|_ property watched | |
|________|____ old and new value
In the callback you can do whatever.
In this example, we can see this effect (Check the jsFiddle) :
var obj = { prop: 123 };
obj.watch('prop', function(propertyName, oldValue, newValue){
console.log('Old value is '+oldValue); // 123
console.log('New value is '+newValue); // 456
});
obj.prop = 456;
When obj change, it activates the watch listener.
You have more information in this link : http://james.padolsey.com/javascript/monitoring-dom-properties/

I wrote the following Gist a little while ago, which allows to listen for custom events cross browser (including IE8+).
Have a look at how I'm listening for onpropertychange on IE8.
util.listenToCustomEvents = function (event_name, callback) {
if (document.addEventListener) {
document.addEventListener(event_name, callback, false);
} else {
document.documentElement.attachEvent('onpropertychange', function (e) {
if(e.propertyName == event_name) {
callback();
}
}
};
I'm not sure the IE8 solution works cross browser, but you could set a fake eventlistener on the property value of your input and run a callback once the value of value changes triggered by onpropertychange.

This is an old question, but with the newish JS Proxy object, triggering an event on a value change is pretty easy:
let proxyInput = new Proxy(input, {
set(obj, prop, value) {
obj[prop] = value;
if(prop === 'value'){
let event = new InputEvent('input', {data: value})
obj.dispatchEvent(event);
}
return true;
}
})
input.addEventListener('input', $event => {
output.value = `Input changed, new value: ${$event.data}`;
});
proxyInput.value = 'thing'
window.setTimeout(() => proxyInput.value = 'another thing', 1500);
<input id="input">
<output id="output">
This creates a JS proxy object based on the original input DOM object. You can interact with the proxy object in the same way you'd interact with the origin DOM object. The difference is that we've overridden the setter. When the 'value' prop is changed, we carry out the normal, expected operation, obj[prop] = value, but then if the prop's value is 'value' we fire a custom InputEvent.
Note that you can fire whatever kind of event you'd like with new CustomEvent or new Event. "change" might be more appropriate.
Read more on proxies and custom events here:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy
https://developer.mozilla.org/en-US/docs/Web/Guide/Events/Creating_and_triggering_events
Caniuse:
https://caniuse.com/#search=proxy

Find out if html form has changed

Using jquery I've added a change handler to a form.
This works when any input is changed BUT only if the user manually changes an input and not when some other code changes the input.
Is there any way to detect if a form has changed even if its inputs are changed by code?

Yes, there seems to be some confusion over this. In an ideal world you would expect the onchange event to happen whenever the inputs change but thats not what happens. I'm sure for good reasons to - maybe not.
One way I've overcome this obstacle is to capture the form state into a variable just after displaying it and then just before submitting it to check if the state has changed and to act accordingly.
An easy state to store is what the serialize function returns. An easy place to store the state is using the data functionality. Both serialize and data are available with jquery.
Of course you can use other different forms of state (some form of hash) or storage for this state (standard global variable for example).
Here is some prototype code:
If your form id is 'xform' then you can call the following code when the form has displayed:
$('#xform').data('serialize',$('#xform').serialize());
And then, when you need to check, for example just before a button submit you can use:
if($('#xform').serialize()!=$('#xform').data('serialize')){
// Form has changed!!!
}
You could wrap all this up into a copy & paste javascript snippet that will give you a formHasChanged() function to call wherever you need it (NOT TESTED):
$(function() {
$('#xform').data('serialize',$('#xform').serialize());
});
function formHasChanged(){
if($('#xform').serialize()!=$('#xform').data('serialize')){
return(true);
}
return(false);
}
But I'll stop here otherwise I'll create yet another jquery plugin.

Serializing the form is certainly an option, but it will not work if:
you want to know which fields have changed
it only needs to check a subset of the fields
dynamically adding or removing fields.
Fortunately, every form element has a default value associated with its object:
input, textarea : defaultValue
checkbox, radio : defaultChecked
select: defaultSelected
for ex: to ckeck if input or textarea has changed:
var changed = false;
$(":text,textarea").each(function(){
changed = this.value != this.defaultValue;
return !changed; // return if at least one control has changed value
});

This is easily achieved in JavaScript without jQuery. initChangeDetection() can be called multiple times:
function initChangeDetection(form) {
Array.from(form).forEach(el => el.dataset.origValue = el.value);
}
function formHasChanges(form) {
return Array.from(form).some(el => 'origValue' in el.dataset && el.dataset.origValue !== el.value);
}
Test on JS Bin
For older browsers that don't support newer arrow/array functions:
function initChangeDetection(form) {
for (var i=0; i<form.length; i++) {
var el = form[i];
el.dataset.origValue = el.value;
}
}
function formHasChanges(form) {
for (var i=0; i<form.length; i++) {
var el = form[i];
if ('origValue' in el.dataset && el.dataset.origValue !== el.value) {
return true;
}
}
return false;
}

Not in a regular way.
You can change with input and then trigger the change event.
$('#inputId').val('foo').trigger('change');
or with this:
$('#inputId').val('foo').change();

Here is what i did (i found my solution using zaf's answer)
$("form").change(function() {
$(this).data("changed","true");
});
$("input[type='submit']").click(function() {
if($("form").data("changed") == "true") {
var discard = confirm("Some unsaved changes. Discard them ?");
if(!discard) return false;
}
});

Try onchange attribute
According to W3c it should trigger anytime the content of an element, the selection, or the checked state have changed.