KnockoutJS - Linking value from a input to a datalist value
I want to display the name property, but I need to store the Id.
Since there is currently no Knockout binding for HTML5 <datalist>, I made one.
I tried to borrow as much as I could from the select binding, so there is support for options, optionsText and optionsValue. You can specify a target observable via value.
ko.bindingHandlers.datalist = (function () {
function getVal(rawItem, prop) {
var item = ko.unwrap(rawItem);
return item && prop ? ko.unwrap(item[prop]) : item;
}
function findItem(options, prop, ref) {
return ko.utils.arrayFirst(options, function (item) {
return ref === getVal(item, prop);
});
}
return {
init: function (element, valueAccessor, allBindingsAccessor) {
var setup = valueAccessor(),
textProperty = ko.unwrap(setup.optionsText),
valueProperty = ko.unwrap(setup.optionsValue),
dataItems = ko.unwrap(setup.options),
myValue = setup.value,
koValue = allBindingsAccessor().value,
datalist = document.createElement("DATALIST");
// create an associated <datalist> element
datalist.id = element.getAttribute("list");
document.body.appendChild(datalist);
// when the value is changed, write to the associated myValue observable
function onNewValue(newVal) {
var dataItems = ko.unwrap(setup.options),
selectedItem = findItem(dataItems, textProperty, newVal),
newValue = selectedItem ? getVal(selectedItem, valueProperty) : void 0;
if (ko.isWriteableObservable(myValue)) {
myValue(newValue);
}
}
// listen for value changes
// - either via KO's value binding (preferred) or the change event
if (ko.isSubscribable(koValue)) {
koValue.subscribe(onNewValue);
} else {
ko.utils.registerEventHandler(element, "change", function () {
onNewValue(this.value);
});
}
// init the element's value
// - either via the myValue observable (preferred) or KO's value binding
if (ko.isObservable(myValue) && myValue()) {
element.value = getVal(findItem(dataItems, valueProperty, myValue()), textProperty);
} else if (ko.isObservable(koValue) && koValue()) {
onNewValue(koValue());
}
},
update: function (element, valueAccessor) {
var setup = valueAccessor(),
datalist = element.list,
dataItems = ko.unwrap(setup.options),
textProperty = ko.unwrap(setup.optionsText);
// rebuild list of options when an underlying observable changes
datalist.innerHTML = "";
ko.utils.arrayForEach(dataItems, function (item) {
var option = document.createElement("OPTION");
option.value = getVal(item, textProperty);
datalist.appendChild(option);
});
ko.utils.triggerEvent(element, "change");
}
};
})();
I hope I got most of this right. Corrections and improvement suggestions are welcome.
You would use it like this:
<input list="company" data-bind="datalist: {
options: companies,
optionsValue: 'id',
optionsText: 'name',
value: selectedCompany
}" />
Notes.
- There is no need to create a separate
<datalist>in the HTML. The custom binding does that for you. - You must, however, supply the
list=""attribute of the<input>element. I found no way of dynamically setting that in JavaScript so far. valueis optional, but if you supply it, it must be an observable.- You can still use the original
valuebinding outside ofdatalist. It will contain whatever text the<input>displays (no surprises there). However, writing to the built-in value also updates thedatalistvalue, and the other way around. - The
datalistvalue has precedence and will overwrite the built-in value upon view model init. After that they stay in sync. optionsshould be an array (plain old or observable) of objects — companies in this case).optionsTextandoptionsValueare strings that should map to properties on your options.- You do not have to use
optionsValue— in that case the entire object (a single company) would be stored invalue. I would prefer that over storing only the ID. - Currently the set-up reacts to the
changeevent. That means your view model won't update until you leave the input field. - Tested on Chrome 32, YMMV. As I said, comments and corrections are welcome.
Below is a demo, copied from the original fiddle.
function main() {
function Company(company) {
this.id = company.Id;
this.name = company.Name;
this.state = company.State.name;
}
function ViewModel(sampleData) {
var self = this;
self.companies = ko.observableArray();
ko.utils.arrayForEach(sampleData, function (companyData) {
self.companies.push(new Company(companyData));
});
// KO's "value" binding _can_ supply a start value
self.val = ko.observable("Microsoft");
// ... but it is overridden by datalist's "value" binding - in any case you can use both
self.selectedCompany = ko.observable(1);
}
// -----------------------------------------------------------------------------------
ko.applyBindings(new ViewModel([{
Id: 1,
Name: "Apple",
State: {
name: "California"
}
}, {
Id: 2,
Name: "Microsoft",
State: {
name: "Washington"
}
}, {
Id: 3,
Name: "IBM",
State: {
name: "New York"
}
}]));
}
// -----------------------------------------------------------------------------------
ko.bindingHandlers.datalist = (function () {
function getVal(rawItem, prop) {
var item = ko.unwrap(rawItem);
return item && prop ? ko.unwrap(item[prop]) : item;
}
function findItem(options, prop, ref) {
return ko.utils.arrayFirst(options, function (item) {
return ref === getVal(item, prop);
});
}
return {
init: function (element, valueAccessor, allBindingsAccessor) {
var setup = valueAccessor(),
textProperty = ko.unwrap(setup.optionsText),
valueProperty = ko.unwrap(setup.optionsValue),
dataItems = ko.unwrap(setup.options),
myValue = setup.value,
koValue = allBindingsAccessor().value,
datalist = document.createElement("DATALIST");
// create an associated <datalist> element
datalist.id = element.getAttribute("list");
document.body.appendChild(datalist);
// when the value is changed, write to the associated myValue observable
function onNewValue(newVal) {
var dataItems = ko.unwrap(setup.options),
selectedItem = findItem(dataItems, textProperty, newVal),
newValue = selectedItem ? getVal(selectedItem, valueProperty) : void 0;
if (ko.isWriteableObservable(myValue)) {
myValue(newValue);
}
}
// listen for value changes
// - either via KO's value binding (preferred) or the change event
if (ko.isSubscribable(koValue)) {
koValue.subscribe(onNewValue);
} else {
ko.utils.registerEventHandler(element, "change", function () {
onNewValue(this.value);
});
}
// init the element's value
// - either via the myValue observable (preferred) or KO's value binding
if (ko.isObservable(myValue) && myValue()) {
element.value = getVal(findItem(dataItems, valueProperty, myValue()), textProperty);
} else if (ko.isObservable(koValue) && koValue()) {
onNewValue(koValue());
}
},
update: function (element, valueAccessor) {
var setup = valueAccessor(),
datalist = element.list,
dataItems = ko.unwrap(setup.options),
textProperty = ko.unwrap(setup.optionsText);
// rebuild list of options when an underlying observable changes
datalist.innerHTML = "";
ko.utils.arrayForEach(dataItems, function (item) {
var option = document.createElement("OPTION");
option.value = getVal(item, textProperty);
datalist.appendChild(option);
});
ko.utils.triggerEvent(element, "change");
}
};
})();
main();.hint {
color: silver;
font-size: 80%;
}<script src="https://cdnjs.cloudflare.com/ajax/libs/knockout/3.0.0/knockout-min.js"></script>
<input list="company" type="text" placeholder="Select a company..." data-bind="value: val, datalist: {
options: companies,
optionsValue: 'id', /* try removing 'optionsValue' and see what happens to the view model */
optionsText: 'name',
value: selectedCompany
}" />
<span class="hint">(note the "change" event occurs after the field loses focus!)</span>
<hr />
<p>View Model:</p>
<pre data-bind="text: ko.toJSON($root, null, 2)"></pre>