source: Dev/trunk/src/client/dojo/has.js @ 485

define(["require", "module"], function(require, module){
        // module:
        //              dojo/has
        // summary:
        //              Defines the has.js API and several feature tests used by dojo.
        // description:
        //              This module defines the has API as described by the project has.js with the following additional features:
        //
        //              - the has test cache is exposed at has.cache.
        //              - the method has.add includes a forth parameter that controls whether or not existing tests are replaced
        //              - the loader's has cache may be optionally copied into this module's has cahce.
        //
        //              This module adopted from https://github.com/phiggins42/has.js; thanks has.js team!

        // try to pull the has implementation from the loader; both the dojo loader and bdLoad provide one
        // if using a foreign loader, then the has cache may be initialized via the config object for this module
        // WARNING: if a foreign loader defines require.has to be something other than the has.js API, then this implementation fail
        var has = require.has || function(){};
        if(!has("dojo-has-api")){
                var
                        isBrowser =
                                // the most fundamental decision: are we in the browser?
                                typeof window != "undefined" &&
                                typeof location != "undefined" &&
                                typeof document != "undefined" &&
                                window.location == location && window.document == document,

                        // has API variables
                        global = this,
                        doc = isBrowser && document,
                        element = doc && doc.createElement("DiV"),
                        cache = (module.config && module.config()) || {};

                has = function(name){
                        // summary:
                        //              Return the current value of the named feature.
                        //
                        // name: String|Integer
                        //              The name (if a string) or identifier (if an integer) of the feature to test.
                        //
                        // description:
                        //              Returns the value of the feature named by name. The feature must have been
                        //              previously added to the cache by has.add.

                        return typeof cache[name] == "function" ? (cache[name] = cache[name](global, doc, element)) : cache[name]; // Boolean
                };

                has.cache = cache;

                has.add = function(name, test, now, force){
                        // summary:
                        //              Register a new feature test for some named feature.
                        // name: String|Integer
                        //              The name (if a string) or identifier (if an integer) of the feature to test.
                        // test: Function
                        //               A test function to register. If a function, queued for testing until actually
                        //               needed. The test function should return a boolean indicating
                        //              the presence of a feature or bug.
                        // now: Boolean?
                        //               Optional. Omit if `test` is not a function. Provides a way to immediately
                        //               run the test and cache the result.
                        // force: Boolean?
                        //              Optional. If the test already exists and force is truthy, then the existing
                        //              test will be replaced; otherwise, add does not replace an existing test (that
                        //              is, by default, the first test advice wins).
                        // example:
                        //              A redundant test, testFn with immediate execution:
                        //      |       has.add("javascript", function(){ return true; }, true);
                        //
                        // example:
                        //              Again with the redundantness. You can do this in your tests, but we should
                        //              not be doing this in any internal has.js tests
                        //      |       has.add("javascript", true);
                        //
                        // example:
                        //              Three things are passed to the testFunction. `global`, `document`, and a generic element
                        //              from which to work your test should the need arise.
                        //      |       has.add("bug-byid", function(g, d, el){
                        //      |               // g    == global, typically window, yadda yadda
                        //      |               // d    == document object
                        //      |               // el == the generic element. a `has` element.
                        //      |               return false; // fake test, byid-when-form-has-name-matching-an-id is slightly longer
                        //      |       });

                        (typeof cache[name]=="undefined" || force) && (cache[name]= test);
                        return now && has(name);
                };

                // since we're operating under a loader that doesn't provide a has API, we must explicitly initialize
                // has as it would have otherwise been initialized by the dojo loader; use has.add to the builder
                // can optimize these away iff desired
                has.add("host-browser", isBrowser);
                has.add("host-node", (typeof process == "object" && process.versions && process.versions.node && process.versions.v8));
                has.add("host-rhino", (typeof load == "function" && (typeof Packages == "function" || typeof Packages == "object")));
                has.add("dom", isBrowser);
                has.add("dojo-dom-ready-api", 1);
                has.add("dojo-sniff", 1);
        }

        if(has("host-browser")){
                // Common application level tests
                has.add("dom-addeventlistener", !!document.addEventListener);
                has.add("touch", "ontouchstart" in document || window.navigator.msMaxTouchPoints > 0);
                // I don't know if any of these tests are really correct, just a rough guess
                has.add("device-width", screen.availWidth || innerWidth);

                // Tests for DOMNode.attributes[] behavior:
                //       - dom-attributes-explicit - attributes[] only lists explicitly user specified attributes
                //       - dom-attributes-specified-flag (IE8) - need to check attr.specified flag to skip attributes user didn't specify
                //       - Otherwise, in IE6-7. attributes[] will list hundreds of values, so need to do outerHTML to get attrs instead.
                var form = document.createElement("form");
                has.add("dom-attributes-explicit", form.attributes.length == 0); // W3C
                has.add("dom-attributes-specified-flag", form.attributes.length > 0 && form.attributes.length < 40);    // IE8
        }

        has.clearElement = function(element){
                // summary:
                //       Deletes the contents of the element passed to test functions.
                element.innerHTML= "";
                return element;
        };

        has.normalize = function(id, toAbsMid){
                // summary:
                //       Resolves id into a module id based on possibly-nested tenary expression that branches on has feature test value(s).
                //
                // toAbsMid: Function
                //       Resolves a relative module id into an absolute module id
                var
                        tokens = id.match(/[\?:]|[^:\?]*/g), i = 0,
                        get = function(skip){
                                var term = tokens[i++];
                                if(term == ":"){
                                        // empty string module name, resolves to 0
                                        return 0;
                                }else{
                                        // postfixed with a ? means it is a feature to branch on, the term is the name of the feature
                                        if(tokens[i++] == "?"){
                                                if(!skip && has(term)){
                                                        // matched the feature, get the first value from the options
                                                        return get();
                                                }else{
                                                        // did not match, get the second value, passing over the first
                                                        get(true);
                                                        return get(skip);
                                                }
                                        }
                                        // a module
                                        return term || 0;
                                }
                        };
                id = get();
                return id && toAbsMid(id);
        };

        has.load = function(id, parentRequire, loaded){
                // summary:
                //              Conditional loading of AMD modules based on a has feature test value.
                // id: String
                //              Gives the resolved module id to load.
                // parentRequire: Function
                //              The loader require function with respect to the module that contained the plugin resource in it's
                //              dependency list.
                // loaded: Function
                //       Callback to loader that consumes result of plugin demand.

                if(id){
                        parentRequire([id], loaded);
                }else{
                        loaded();
                }
        };

        return has;
});