The goal of this blog post is to describe how templates work in
the WinJS library. In particular, you learn how to use a template to display both a single item and an array of items. You also learn how to load a template from an external file.
Why use Templates?
Imagine that you want to display a list of products in a page.
The following code is bad:
var products = [
{ name: "Tesla", price: 80000 },
{ name: "VW Rabbit", price: 200 },
{ name: "BMW", price: 60000 }
];
var productsHTML = "";
for (var i = 0; i < products.length; i++) {
productsHTML += "<h1>Product Details</h1>"
+ "<div>Product Name: " + products[i].name + "</div>"
+ "<div>Product Price: " + products[i].price + "</div>";
}
document.getElementById("productContainer").innerHTML = productsHTML;
In
the code above, an array of products is displayed by creating a for..next loop which loops through each element in
the array. A string which represents a list of products is built through concatenation.
The code above is a designer’s nightmare. You cannot modify
the appearance of
the list of products without modifying
the JavaScript code.
A much better approach is to use a template like this:
<div id="productTemplate">
<h1>Product Details</h1>
<div>
Product Name:
<span data-win-bind="innerText:name"></span>
</div>
<div>
Product Price:
<span data-win-bind="innerText:price"></span>
</div>
</div>
A template is simply a fragment of HTML that contains placeholders. Instead of displaying a list of products by concatenating together a string, you can render a template for each product.
Creating a Simple Template
Let’s start by using a template to render a single product.
The following HTML page contains a template and a placeholder for rendering
the template:
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Application1</title>
<!-- WinJS references -->
<link href="//Microsoft.WinJS.0.6/css/ui-dark.css" rel="stylesheet">
<script src="//Microsoft.WinJS.0.6/js/base.js"></script>
<script src="//Microsoft.WinJS.0.6/js/ui.js"></script>
<!-- Application1 references -->
<link href="/css/default.css" rel="stylesheet">
<script src="/js/default.js"></script>
</head>
<body>
<!-- Product Template -->
<div id="productTemplate">
<h1>Product Details</h1>
<div>
Product Name:
<span data-win-bind="innerText:name"></span>
</div>
<div>
Product Price:
<span data-win-bind="innerText:price"></span>
</div>
</div>
<!-- Place where Product Template is Rendered -->
<div id="productContainer"></div>
</body>
</html>
In
the page above,
the template is defined in a DIV element with
the id productTemplate.
The contents of
the productTemplate are not displayed when
the page is opened in
the browser.
The contents of a template are automatically hidden when you convert
the productTemplate into a template in your JavaScript code.
Notice that
the template uses data-win-bind attributes to display
the product name and price properties. You can use both data-win-bind and data-win-bindsource attributes within a template. To learn more about these attributes, see my earlier blog post on WinJS data binding:
http://stephenwalther.com/blog/archive/2012/02/26/windows-web-applications-declarative-data-binding.aspx
The page above also includes a DIV element named productContainer.
The rendered template is added to this element.
Here’s
the code for
the default.js script which creates and renders
the template:
(function () {
"use strict";
var app = WinJS.Application;
app.onactivated = function (eventObject) {
if (eventObject.detail.kind === Windows.ApplicationModel.Activation.ActivationKind.launch) {
var product = {
name: "Tesla",
price: 80000
};
var productTemplate = new WinJS.Binding.Template(document.getElementById("productTemplate"));
productTemplate.render(product, document.getElementById("productContainer"));
}
};
app.start();
})();
In
the code above, a single product object is created with
the following line of code:
var product = {
name: "Tesla",
price: 80000
};
Next,
the productTemplate element from
the page is converted into an actual WinJS template with
the following line of code:
var productTemplate = new WinJS.Binding.Template(document.getElementById("productTemplate"));
The template is rendered to
the templateContainer element with
the following line of code:
productTemplate.render(product, document.getElementById("productContainer"));
The result of this work is that
the product details are displayed:
Notice that you do not need to call WinJS.Binding.processAll().
The Template render() method takes care of
the binding for you.
Displaying an Array in a Template
If you want to display an array of products using a template then you simply need to create a for..next loop and iterate through
the array calling
the Template render() method for each element.
(function () {
"use strict";
var app = WinJS.Application;
app.onactivated = function (eventObject) {
if (eventObject.detail.kind === Windows.ApplicationModel.Activation.ActivationKind.launch) {
var products = [
{ name: "Tesla", price: 80000 },
{ name: "VW Rabbit", price: 200 },
{ name: "BMW", price: 60000 }
];
var productTemplate = new WinJS.Binding.Template(document.getElementById("productTemplate"));
var productContainer = document.getElementById("productContainer");
var i, product;
for (i = 0; i < products.length; i++) {
product = products[i];
productTemplate.render(product, productContainer);
}
}
};
app.start();
})();
After each product in
the array is rendered with
the template,
the result is appended to
the productContainer element.
No changes need to be made to
the HTML page discussed in
the previous section to display an array of products instead of a single product.
The same product template can be used in both scenarios.
Rendering an HTML TABLE with a Template
When using
the WinJS library, you create a template by creating an HTML element in your page. One drawback to this approach of creating templates is that your templates are part of your HTML page. In order for your HTML page to validate,
the HTML within your templates must also validate.
This means, for example, that you cannot enclose a single HTML table row within a template.
The following HTML is invalid because you cannot place a TR element directly within
the body of an HTML document:
<!-- Product Template -->
<tr>
<td data-win-bind="innerText:name"></td>
<td data-win-bind="innerText:price"></td>
</tr>
This template won’t validate because, in a valid HTML5 document, a TR element must appear within a THEAD or TBODY element. Instead, you must create
the entire TABLE element in
the template.
The following HTML page illustrates how you can create a template which contains a TR element:
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Application1</title>
<!-- WinJS references -->
<link href="//Microsoft.WinJS.0.6/css/ui-dark.css" rel="stylesheet">
<script src="//Microsoft.WinJS.0.6/js/base.js"></script>
<script src="//Microsoft.WinJS.0.6/js/ui.js"></script>
<!-- Application1 references -->
<link href="/css/default.css" rel="stylesheet">
<script src="/js/default.js"></script>
</head>
<body>
<!-- Product Template -->
<div id="productTemplate">
<table>
<tbody>
<tr>
<td data-win-bind="innerText:name"></td>
<td data-win-bind="innerText:price"></td>
</tr>
</tbody>
</table>
</div>
<!-- Place where Product Template is Rendered -->
<table>
<thead>
<tr>
<th>Name</th><th>Price</th>
</tr>
</thead>
<tbody id="productContainer">
</tbody>
</table>
</body>
</html>
In
the HTML page above,
the product template includes TABLE and TBODY elements:
<!-- Product Template -->
<div id="productTemplate">
<table>
<tbody>
<tr>
<td data-win-bind="innerText:name"></td>
<td data-win-bind="innerText:price"></td>
</tr>
</tbody>
</table>
</div>
We discard these elements when we render
the template.
The only reason that we include
the TABLE and THEAD elements in
the template is to make
the HTML page validate as valid HTML5 markup.
Notice that
the productContainer (the target of
the template) in
the page above is a TBODY element. We want to add
the rows rendered by
the template to
the TBODY element in
the page.
The productTemplate is rendered in
the default.js file:
(function () {
"use strict";
var app = WinJS.Application;
app.onactivated = function (eventObject) {
if (eventObject.detail.kind === Windows.ApplicationModel.Activation.ActivationKind.launch) {
var products = [
{ name: "Tesla", price: 80000 },
{ name: "VW Rabbit", price: 200 },
{ name: "BMW", price: 60000 }
];
var productTemplate = new WinJS.Binding.Template(document.getElementById("productTemplate"));
var productContainer = document.getElementById("productContainer");
var i, product, row;
for (i = 0; i < products.length; i++) {
product = products[i];
productTemplate.render(product).then(function (result) {
row = WinJS.Utilities.query("tr", result).get(0);
productContainer.appendChild(row);
});
}
}
};
app.start();
})();
When
the product template is rendered,
the TR element is extracted from
the rendered template by using
the WinJS.Utilities.query() method. Next, only
the TR element is added to
the productContainer:
productTemplate.render(product).then(function (result) {
row = WinJS.Utilities.query("tr", result).get(0);
productContainer.appendChild(row);
});
I discuss
the WinJS.Utilities.query() method in depth in a previous blog entry:
http://stephenwalther.com/blog/archive/2012/02/23/windows-web-applications-query-selectors.aspx
When everything gets rendered,
the products are displayed in an HTML table:
You can see
the actual HTML rendered by looking at
the Visual Studio DOM Explorer window:
Loading an External Template
Instead of embedding a template in an HTML page, you can place your template in an external HTML file. It makes sense to create a template in an external file when you need to use
the same template in multiple pages. For example, you might need to use
the same product template in multiple pages in your application.
The following HTML page does not contain a template. It only contains a container that will act as a target for
the rendered template:
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Application1</title>
<!-- WinJS references -->
<link href="//Microsoft.WinJS.0.6/css/ui-dark.css" rel="stylesheet">
<script src="//Microsoft.WinJS.0.6/js/base.js"></script>
<script src="//Microsoft.WinJS.0.6/js/ui.js"></script>
<!-- Application1 references -->
<link href="/css/default.css" rel="stylesheet">
<script src="/js/default.js"></script>
</head>
<body>
<!-- Place where Product Template is Rendered -->
<div id="productContainer"></div>
</body>
</html>
The template is contained in a separate file located at
the path /templates/productTemplate.html:
Here’s
the contents of
the productTemplate.html file:
<!-- Product Template -->
<div id="productTemplate">
<h1>Product Details</h1>
<div>
Product Name:
<span data-win-bind="innerText:name"></span>
</div>
<div>
Product Price:
<span data-win-bind="innerText:price"></span>
</div>
</div>
Notice that
the template file only contains
the template and not
the standard opening and closing HTML elements. It is an HTML fragment.
If you prefer, you can include all of
the standard opening and closing HTML elements in your external template – these elements get stripped away automatically:
<html>
<head><title>product template</title></head>
<body>
<!-- Product Template -->
<div id="productTemplate">
<h1>Product Details</h1>
<div>
Product Name:
<span data-win-bind="innerText:name"></span>
</div>
<div>
Product Price:
<span data-win-bind="innerText:price"></span>
</div>
</div>
</body>
</html>
Either approach – using a fragment or using a full HTML document — works fine.
Finally,
the following default.js file loads
the external template, renders
the template for each product, and appends
the result to
the product container:
(function () {
"use strict";
var app = WinJS.Application;
app.onactivated = function (eventObject) {
if (eventObject.detail.kind === Windows.ApplicationModel.Activation.ActivationKind.launch) {
var products = [
{ name: "Tesla", price: 80000 },
{ name: "VW Rabbit", price: 200 },
{ name: "BMW", price: 60000 }
];
var productTemplate = new WinJS.Binding.Template(null, { href: "/templates/productTemplate.html" });
var productContainer = document.getElementById("productContainer");
var i, product, row;
for (i = 0; i < products.length; i++) {
product = products[i];
productTemplate.render(product, productContainer);
}
}
};
app.start();
})();
The path to
the external template is passed to
the constructor for
the Template class as one of
the options:
var productTemplate = new WinJS.Binding.Template(null, {href:"/templates/productTemplate.html"});
When a template is contained in a page then you use
the first parameter of
the WinJS.Binding.Template constructor to represent
the template – instead of null, you pass
the element which contains
the template. When a template is located in an external file, you pass
the href for
the file as part of
the second parameter for
the WinJS.Binding.Template constructor.
Summary
The goal of this blog entry was to describe how you can use WinJS templates to render either a single item or an array of items to a page. We also explored two advanced topics. You learned how to render an HTML table by extracting
the TR element from a template. You also learned how to place a template in an external file.
