How to apply binding and persist input value using Knockout JS?

Kees C. Bakker

I am building an HTML/KnockoutJS application. My web server returns a form with input fields and information. When I update the model and execute ko.applyBindings, the input value is naturally overwritten by the model.

Is there a way to automatically load the input field's data ko.applyBindingsinto the model ?

Example : https://jsfiddle.net/KeesCBakker/p7ygq5y2/1/ _

HTML：

Title: <input data-bind="textInput: title" value="MyTitle" placeholder="Nothing here!" /><br/>
Text: <input data-bind="textInput: text" value="MyText" placeholder="Nothing here!" /><br/>
<button id="bind">Bind!</button>

JS：

ko.bindingHandlers.initFromInput = {
  init: function(element, valueAccessor) {
    valueAccessor()(element.value);
  }
};

function Model() {
  this.title = ko.observable();
  this.text = ko.observable();
}

document.getElementById('bind').onclick = function() {

  var model = new Model();
  ko.applyBindings(model);

};
clean_coding

You can use a custom binding to tell Knockout to use the input value as the default, like this:

ko.bindingHandlers.initFromInput = {
    init: function(element, valueAccessor) {
        valueAccessor()(element.value);
    }
};

Here is a jsfiddle : http://jsfiddle.net/kv3zras3/3/

edit:

With the new binding, your data binding should look like this:

<input data-bind="initFromInput: title, value: title" value="MyTitle" placeholder="Nothing here!" />
<input data-bind="initFromInput: text, value:text" value="MyText" placeholder="Nothing here!" />

edit:

There is a better way to do it if you make the bindings look like this:

var origValueInput = ko.bindingHandlers.value.init;
ko.bindingHandlers.value.init = function(element, valueAccessor, allBindings) {
    if (allBindings.has('initValueFromInput')) {
        valueAccessor()(element.value);
    }
    origValueInput.apply(this, arguments);
};

You can write data binding like this:

<input value="MyTitle" data-bind="initValueFromInput, value: title"/>
<input value="MyText" data-bind="initValueFromInput, value: text"/>

Here is a fiddle : https://jsfiddle.net/yy51kok5/

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