has.md

layout	title
doc	requirejs-dplugins/has

requirejs-dplugins/has

requirejs-dplugins/has provides an extensible API to manage feature detection. It also implements the requirejs plugin api to provide conditional module loading.

It is based on the conventions in the has.js project.

Note: This plugin does NOT include any feature tests.

Table of Contents

Features
Adding tests
Use as module
Use as plugin
Build

Features

• lazy evaluation: Tests are only evaluated when they are required by the application.
• test result caching: tests results are stored for later use to minimize the impact on resources.
• static configuration: Tests can be set statically using requirejs configuration, providing support for configuration flag.
• requirejs plugin: Use ternary operator to conditionally load modules.

Adding tests

Since the plugin itself does not include any tests, the first thing to do is add one.

Using has.add()

The plugin provides an add function to add new tests, with the following signature:

has.add(name, test, now, force)

1. name (String): The test name.
2. test (Boolean or Function): The test function or directly a Boolean value. The test function will be call with a single global argument pointing to the global scope.
3. now (Boolean): If true, evaluate the test function now instead of when it will be needed.
4. force (Boolean): If true, add the test even if a test with the same name already exists.

Sample

define(["requirejs-dplugins/has"], function (has) {
	// using a boolean directly
	has.add("host-browser", typeof window !== "undefined");

	// using a test function and overwriting previous tests
	has.add("host-browser", function (global) {
		return global.window !== undefined;
	}, false, true);
});

Using static configuration

The plugin will look for static configuration in a hashmap provided through requirejs module configuration.

Sample

require.config({
	config: {
		"requirejs-dplugins/has": {
			// Create a bidi flag.
			bidi: true
		}
	}
});

Use as module

To access the tests, the plugin exports a main function taking a test name as argument and returning the test result.

Sample

define(["requirejs-dplugins/has"], function (has) {
	if (has("bidi")) {
		// Do something special to support bidi
	}
});

Use as plugin

Ternary operator can be used to conditionally load modules. It uses the following syntax:

test?moduleA:moduleB

If test return true, moduleA will be loaded, otherwise it will be moduleB. Note that moduleA and moduleB are optional and if the expression doesn't resolve to a module, the plugin returns undefined.

Ternary operation can be chained to run another test if the first one fails.

test1?moduleA:test2?moduleB:moduleC

If test1 is true, the plugin loads moduleA. If test1 is false but test2 is true, the plugin loads moduleB. If test1 is false and test2 is false, the plugin loads moduleC.

Sample

define(["requirejs-dplugins/has!bidi?./bidiWidget:./Widget"], function (widget) {
	// Do something with the widget
});

Build

Has flag can be specified at build time using the static configuration. If a flag is undefined at build time, then all the possible modules will be added to the layer. If a flag was set to true or false, the build will resolve the ternary condition and include only the needed modules in the layer.