Develop Reference

2 way data binding in JavaScript

Two-way data binding refers to the ability to bind changes to an object’s properties to changes in the UI, and vice-versa.
Can we achieve 2-way data-binding with JavaScript?
Especially 2 Way Data Binding without Frameworks.

When an input is changed update the value, add a setter to the value which sets the inputs content. E.g this element:
<input id="age">
And some js:
var person = (function(el){
return {
set age(v){
el.value = v;
},
get age(){
return el.value;
}
};
})(document.getElementById("age"));
So you can do:
person.age = 15;
And the input will change. Changing the input changes person.age

Yes, we can achieve the two way data binding using pure javascript.
twoWay=function(event) {
var elem = document.getElementsByClassName(event.currentTarget.className);
for(var key in elem){
elem[key].value=event.currentTarget.value;
}
}
You can check the jsfiddle.

Simple and working approach to two-way binding, only using vanilla JS.
<!-- index.html -->
<form action="#" onsubmit="vm.onSubmit(event, this)">
<input onchange="vm.username=this.value" type="text" id="Username">
<input type="submit" id="Submit">
</form>
<script src="vm.js"></script>
// vm.js - vanialla JS
let vm = {
_username: "",
get username() {
return this._username;
},
set username(value) {
this._username = value;
},
onSubmit: function (event, element) {
console.log(this.username);
}
}
JS Getters and Setters are quite nice for this - especially when you look at the browser support.

Yes indeed.
There are frameworks like angular Js which provides full support for two way data binding.
And if you want to achieve the same in vanilla js you can bind value into view
Eg. document.getElementById('test').value="This is a Test"
And to bind view value to the controller you can trigger onchange event in html.
<Input type="text" id="test" onchange="Func()">

LemonadeJS is another micro-library (4K), with no dependencies worth looking at.
https://lemonadejs.net
https://github.com/lemonadejs/lemonadejs

Adding a little elaboration to Jonas Wilms answer, here's a sample without currying and also adds event binding for a full two way bind.
// Property binding
var person = {
set name(v) {
document.getElementById('name').value = v;
},
get name() {
return document.getElementById('name').value;
},
set age(v) {
document.getElementById('age').value = v;
},
get age() {
return document.getElementById('age').value;
}
};
// You can now set values as such
person.name = 'Cesar';
person.age = 12;
// Event binding completes the two way
function logToConsole(event) {
console.log(event.target.value);
}
// You can set person.name or person.age in console as well.
<label for="name">Name: </label><input id="name" onkeyup="logToConsole(event)">
<label for="age">Age: </label><input id="age" onkeyup="logToConsole(event)">

Would you mind if it would be a small component for databinding tasks that provides enough convenient databinding definition commands. I did it with databindjs. e.g.
// Lets assume that there is just simple form (target)
var simpleForm = {
input: $('.simple .input-value'),
output: $('.simple .output-value')
};
// And here is the simple model object (source)
var model = {
text: 'initial value'
};
// Lets set two directional binding between [input] <-> [text]
var simpleBinding = bindTo(simpleForm, () => model, {
'input.val': 'text', // bind to user input
'output.text': 'text' // simple region that will react on user input
});
// This command will sync values from source to target (from model to view)
updateLayout(simpleBinding);
subscribeToChange(simpleBinding, () => {
$('.simple .console').html(JSON.stringify(model));
});
// Just initialize console from default model state
$('.simple .console').html(JSON.stringify(model));
The full solution here.
You can check the full implementation of the databinding core on github

How do I reset a form in angularjs?

See Fiddle: http://jsfiddle.net/hejado/7bqjqc2w/
I'm trying to form.reset() my form using angular.
HTML:
<div ng-controller="formCtrl">
<form name="resetme" id="resetme">
<input ng-model="text" type="text" />
<input file-model="file" type="file" />
<button type="button" ng-click="resetForm()">reset</button>
</form>
</div>
JS:
.controller('formCtrl', function($scope) {
$scope.resetForm = function() {
//$scope.resetme.reset();
document.getElementById('resetme').reset();
};
});
Please note: I'm using this kind of form to ajax-upload a file. The page is not refreshing and I don't want to use any reset-buttons. (I'm using one in the fiddle for simplicity.) I want to call the reset-function after the fileupload is finished (via http success).
I'm using
<input type="file" />
so I can't reassign empty values to all my inputs, because file inputs are readonly.
Calling the reset() function on the DOM element works, but I was told talking to the DOM in angular would be evil, so...
I'd like to know, how this would be done the angular way. I tried naming the form and referencing it via $scope.formname but I'm not able to call Web API functions... (commented line)
How can I achieve this?
UPDATE
After reading some of the answers, I should make clear, that I am using ngModel and a custom directive fileModel to get a hold of the file-object.
Some of the solutions worked in resetting the value of the input field, but the model is not cleared (neither file, nor text). Custom directives are the answer to that, but this kinda exceeds the scope of this question.

I wrote about this topic a couple years ago. I don't know if the Angular team has yet implemented a native form reset directive but you can do so yourself. There are a couple caveats to this implementation: it only works for one model (if you need to support more see the followup post) and the issue of when to initialize the original values. Also, I never tested this with file inputs so I am not sure it would work with those.
There was an issue for this but it was closed due to inactivity. :/
var myApp = angular.module('myApp', []);
myApp.controller('MyCtrl', ['$scope',
function($scope) {
$scope.myModel = {
foo: 'Boop',
bar: 'Beep'
};
$scope.myModelCopy = angular.copy($scope.myModel);
}
]);
myApp.directive('resetDirective', ['$parse',
function($parse) {
return function(scope, element, attr) {
var fn = $parse(attr.resetDirective);
var masterModel = angular.copy(fn(scope));
// Error check to see if expression returned a model
if (!fn.assign) {
throw Error('Expression is required to be a model: ' + attr.resetDirective);
}
element.bind('reset', function(event) {
scope.$apply(function() {
fn.assign(scope, angular.copy(masterModel));
scope.form.$setPristine();
});
// TODO: memoize prevention method
if (event.preventDefault) {
return event.preventDefault();
} else {
return false;
}
});
};
}
]);
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
<body ng-app="myApp">
<div ng-controller="MyCtrl">
<form reset-directive="myModel" name="form">
<input type="text" ng-model="myModel.foo" />
<input type="text" ng-model="myModel.bar" />
<input type="reset" value="Reset" />
<pre>myModel: {{ myModel | json }}</pre>
<pre>myModelCopy: {{ myModelCopy | json }}</pre>
<pre>form pristine: {{ form.$pristine }}</pre>
</form>
</div>
</body>

You can try :
reset
$scope.resetForm = function(form) {
//Even when you use form = {} it does not work
form.fieldA = null;
form.fieldB = null;
///more fields
}
Or
$scope.resetForm = function(form) {
//Even when you use form = {} it does not work
angular.copy({},form);
}
See Demo

You'd want to attach ng-model to each of your input fields then null them out via $scope. Either that or make a custom directive

I've just had a similar problem with forms not resetting. Here's what I would do:
In your resetform() function, I would include statements that set both of your ng-models in your input to "". For example:
**HTML**
<input ng-model="text" type="text" />
<input file-model="file" type="file" />
**JS**
.controller('formCtrl', function($scope) {
$scope.resetForm = function() {
$scope.text = "";
$scope.file = null;
};
});
Not certain if this will work for file-models but I'm certain it will remove the text. Best of luck!

If you don't want to use ng-model and proper reset type of button you can use this code, however this is not proper angular way to reset the form but it will work
$scope.reset = function(){
$('form').children('*').each(function(){
$(this).val('');
});
}
Here's the Plunker

To reset the form data use following code :
$scope.resetEmployeeData = function() {
$scope.employeeCred.userName = '';
$scope.employeeCred.employeeNo = '';
$scope.employeeCred.sapNo = '';
$scope.employeeCred.emailD = '';
$scope.employeeCred.mobileNo = '';
**this**.createEmployee.$setPristine();
**this**.createEmployee.$setUntouched();
};
use this rather than $scope.

Enable binding with multiple boolean observable flags

Trying to bind enable state using data-bind based on two flags. We need to enable a input box if flagA is true and also flagB is false.
var viewModel = function () {
var self = this;
self.flagA = ko.observable(true);
self.flagB = ko.observable(false);
self.changeState = function () {
self.flagA(false);
}
}
ko.applyBindings(viewModel);
<script src="https://cdnjs.cloudflare.com/ajax/libs/knockout/3.2.0/knockout-min.js"></script>
<input type='text' data-bind='enable: flagA && !flagB' />
<button data-bind='click:changeState'>changeState</button>
Can any one help me find out why it is not working?
I've tried using a function like enable:function(){flagA && !flagB} to make this work. But it's not working: it does not observe when I change the state using a button.

Because flagA and flagB are observables (which are functions) you need to call them without any argument to get there values if you are using them in an expression:
<input type='text' data-bind='enable: flagA() && !flagB()' />
Demo JSFiddle.

Try to avoid putting logic in your views, it's a bad practice. In order to do this add computed variable
self.isEnabled = ko.computed(function() {
return this.flagA() && !this.flagB()
}, this);
and bind it as usual:
<input type='text' data-bind='enable: isEnabled' />
See fiddle

Preventing Text Submission In Controller Failing

I'm running a simple example from the main page of Angular involving a todo list. I want to prevent the user from submitting a todo when the input field is blank. The problem is when I load the page and the first thing I do is I click inside the input field and press enter, then the blank todo is added the Todo list. However, after that the validation works. I know there are other ways of doing this, but I want to know why this bug exists and how to fix it.
My html below
<form ng-submit="addTodo()">
<input ng-model="todoText" placeholder="Add a todo here" type="text" />
<input class="button" type="submit" value="add">
</form>
My js file
$scope.addTodo = function() {
var text = $scope.todoText;
if (text != "") {
$scope.todos.push({text:$scope.todoText, done:false});
$scope.todoText = '';
}
};

$scope.todoText is undefined , so it passes your condition and then is set to empty string '', based on your model's variables
either do if (!$scope.todoText) { or initialize it to empty string $scope.todoText = '';
in controller:
$scope.todoText = '';
$scope.addTodo = function() {
if ($scope.todoText != "") {
$scope.todos.push({text:$scope.todoText, done:false});
$scope.todoText = '';
}
};

Have you tried using the required attribute in the input?
<input type="text"
ng-model="todoText"
required <------------- prevents submission and marks the view as invalid
size="30"
placeholder="add new todo here" />
Have a try at http://jsfiddle.net/hbulhoes/uBXfN/

copy form to Backbone.js model

I have a form:
<form>
<input type="text" name="email" >
<input type="text" name="phone" >
<input type="button" value="ok" />
</form>
When clicking the button, I'd like to copy the form values to a corresponding model.
I've found Backbone.ModelBinder which will automatically copy values to model whenever the values are changed, but that's not what I want, I just want to copy the values when the button is clicked.

write a custom function into the view where the form is located and bind it to the ok click event:
events: {
...
'click input[name="ok"]': 'copyFormToModel'
...
},
...
copyFormToModel: function() {
var email = $('input[name="email"]').val();
var phone = $('input[name="phone"]').val();
// Perform some sort of validation
this.model.email = email;
this.model.phone = phone;
}
This isn't the prettiest answer, but if you have just one small form in your page, then using some library or plugin might be a bit overkill. If you want to use a plugin or library, then for your case I think backbone-forms could do the trick. It features updating the model bound to the form with a method call rather than every time fields are updated.

This code may be you need：
events: {
...
'click input[value="ok"]': 'collectData2Model'
...
},
...
//suppose employee is your model
collectData2Model: function(e) {
var employee = new Employee();
var attr = {};
$('input').each(function(){
var input = $(this);
attr[input.attr('name')] = input.val();
});
employee.bind('error',function(model,error){
alert(error);
});
// set method will automatically call the model's validate method
employee.set(attr);
}