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Web template structure and instantiation

Structure a template's index.html file and create a new instance of your content with createUnityInstance().
Read time 4 minutesLast updated 7 days ago
Use custom user variables in a template's 
index.html
file and create a new instance of your content with 
createUnityInstance()
.
For information about template variables, JavaScript macros, and conditional directives, refer to Web template variables.
To add a custom Web template, refer to Add a custom Web template.

Custom user variables

When you select a Web template, Unity parses the template and looks for JavaScript macros and conditional directives.
Unity treats JavaScript variables as custom user variables if they're:
  • Used inside JavaScript macros and conditional directives.
  • Not declared in the template code.
  • Not internal pre-processor variables.
Unity automatically adds these custom user variables to the Resolution and Presentation section in the
Player Settings

?

window.
As an example, if you want to control the title of the generated 
index.html
page directly from the Player Settings window, you first need to modify the 
<title>
line of the 
index.html
in your custom template, like this:
<title>{{{ PAGE_TITLE }}}</title>
After you have done this, re-select your custom template. This parses the template again, and a Page Title field appears in the Resolution and Presentation > Web Template section of the Player Settings window.

Image of Resolution and Presentation window with custom template

When you enter text into this field and build your project, the custom variable 
PAGE_TITLE
in the template macro automatically becomes the text in the Page Title field.
If you would like to use custom integer or float variables in your macros, use 
parseInt()
or 
parseFloat()
JavaScript functions in your macros to preprocess string values supplied by the Unity Editor. This is because custom user variables are always assigned a string value.
Note
Underscore characters in variable names display as spaces inside the field to improve readability.

Structure of the index.html file

The 
index.html
contains the code necessary to load the build and should include the following:
  • A 
    <canvas>
    element. Unity runtime uses the 
    <canvas>
    element to render the application.
  • JavaScript code to download the build loader. For example:
var buildUrl = "Build";var loaderUrl = buildUrl + "/{{{ LOADER_FILENAME }}}";var script = document.createElement("script");script.src = loaderUrl;script.onload = () => {  // code for instantiating the build};document.body.appendChild(script);`
In this example, 
{{{ LOADER_FILENAME }}}
is automatically resolved by the template preprocessor when the build is generated.
Alternatively, you can download the build loader using a script tag, for example:
<script src="Build/{{{ LOADER_FILENAME }}}"></script>
  • JavaScript code for instantiating a build. Unity builds are instantiated using the 
    createUnityInstance()
    function, which is defined in the build loader script.

The instantiation function: createUnityInstance()

The 
createUnityInstance()
function creates a new instance of your content. You can use it like this:
createUnityInstance(canvas, config,  onProgress).then(onSuccess).catch(onError);
This function returns a 
Promise
object, where:

Object

Use

canvas
Unity runtime uses the 
canvas
object to render the game.
config
The 
config
object contains the build configuration, such as the code and data URLs, product and company name, and version. For more information on config definition, refer to Web template build configuration and interaction.
onProgress(progress) {...}
The Web loader calls the 
onProgress
callback object every time the download progress updates. This occurs during the initial load of the project and, if Progressive Asset Loading is enabled, during synchronous scene loads when the required assets have not yet finished downloading. The 
progress
argument that comes with the 
onProgress
callback determines the loading progress as a value between 0.0 and 1.0.
onSuccess(unityInstance) {...}
The 
onSuccess
callback is called after the build has successfully instantiated. The created Unity instance object is provided as an argument. This object can be used for interaction with the build.
onError(message) {...}
The 
onError
callback is called if an error occurs during build instantiation. An error message is provided as an argument.
The 
createUnityInstance()
function is defined in the build loader script and is specific to the instantiated build. Therefore, if you're embedding two or more builds in the same HTML document, make sure that the 
createUnityInstance()
function is called from an 
onload
callback of the corresponding build loader script. For more information about the Unity Web Loader, refer to Web Build folder and Web template structure and instantiation.

Additional resources