first commit

README

@@ -0,0 +1,42 @@
+JSON in JavaScript
+
+
+Douglas Crockford
+[email protected]
+
+2010-11-18
+
+
+JSON is a light-weight, language independent, data interchange format.
+See http://www.JSON.org/
+
+The files in this collection implement JSON encoders/decoders in JavaScript.
+
+JSON became a built-in feature of JavaScript when the ECMAScript Programming
+Language Standard - Fifth Edition was adopted by the ECMA General Assembly
+in December 2009. Most of the files in this collection are for applications 
+that are expected to run in obsolete web browsers. For most purposes, json2.js 
+is the best choice.
+
+
+json2.js: This file creates a JSON property in the global object, if there 
+isn't already one, setting its value to an object containing a stringify
+method and a parse method. The parse method uses the eval method to do the
+parsing, guarding it with several regular expressions to defend against
+accidental code execution hazards. On current browsers, this file does nothing,
+prefering the built-in JSON object.
+
+json.js: This file does everything that json2.js does. It also adds a
+toJSONString method and a parseJSON method to Object.prototype. Use of this
+file is not recommended.
+
+json_parse.js: This file contains an alternative JSON parse function that
+uses recursive descent instead of eval.
+
+json_parse_state: This files contains an alternative JSON parse function that
+uses a state machine instead of eval.
+
+cycle.js: This file contains two functions, JSON.decycle and JSON.retrocycle,
+which make it possible to encode cyclical structures and dags in JSON, and to
+then recover them. JSONPath is used to represent the links. 
+http://GOESSNER.net/articles/JsonPath/

cycle.js

@@ -0,0 +1,158 @@
+// cycle.js
+// 2010-11-18
+
+/*jslint forin: true, evil: true */
+
+/*members $ref, apply, call, decycle, hasOwnProperty, length, prototype, push,
+    retrocycle, stringify, test, toString
+*/
+
+if (typeof JSON.decycle !== 'function') {
+    JSON.decycle = function decycle(object) {
+
+// Make a deep copy of an object or array, assuring that there is at most
+// one instance of each object or array in the resulting structure. The
+// duplicate references (which might be forming cycles) are replaced with
+// an object of the form
+//      {$ref: PATH}
+// where the PATH is a JSONPath string that locates the first occurance.
+// So,
+//      var a = [];
+//      a[0] = a;
+//      return JSON.stringify(JSON.decycle(a));
+// produces the string '[{"$ref":"$"}]'.
+
+// JSONPath is used to locate the unique object. $ indicates the top level of
+// the object or array. [NUMBER] or [STRING] indicates a child member or
+// property.
+
+        var objects = [],   // Keep a reference to each unique object or array
+            paths = [];     // Keep the path to each unique object or array
+
+        return (function derez(value, path) {
+
+// The derez recurses through the object, producing the deep copy.
+
+            var i,          // The loop counter
+                name,       // Property name
+                nu;         // The new object or array
+
+            switch (typeof value) {
+            case 'object':
+
+// typeof null === 'object', so get out if this value is not really an object.
+
+                if (!value) {
+                    return null;
+                }
+
+// If the value is an object or array, look to see if we have already
+// encountered it. If so, return a $ref/path object. This is a hard way,
+// linear search that will get slower as the number of unique objects grows.
+
+                for (i = 0; i < objects.length; i += 1) {
+                    if (objects[i] === value) {
+                        return {$ref: paths[i]};
+                    }
+                }
+
+// Otherwise, accumulate the unique value and its path.
+
+                objects.push(value);
+                paths.push(path);
+
+// If it is an array, replicate the array.
+
+                if (Object.prototype.toString.apply(value) === '[object Array]') {
+                    nu = [];
+                    for (i = 0; i < value.length; i += 1) {
+                        nu[i] = derez(value[i], path + '[' + i + ']');
+                    }
+                } else {
+
+// If it is an object, replicate the object.
+
+                    nu = {};
+                    for (name in value) {
+                        if (Object.hasOwnProperty.call(value, name)) {
+                            nu[name] = derez(value[name],
+                                    path + '[' + JSON.stringify(name) + ']');
+                        }
+                    }
+                }
+                return nu;
+            case 'number':
+            case 'string':
+            case 'boolean':
+                return value;
+            }
+        }(object, '$'));
+    };
+}
+
+
+if (typeof JSON.retrocycle !== 'function') {
+    JSON.retrocycle = function retrocycle($) {
+
+// Restore an object that was reduced by decycle. Members whose values are
+// objects of the form
+//      {$ref: PATH}
+// are replaced with references to the value found by the PATH. This will
+// restore cycles. The object will be mutated.
+
+// The eval function is used to locate the values described by a PATH. The
+// root object is kept in a $ variable. A regular expression is used to
+// assure that the PATH is extremely well formed. The regexp contains nested
+// * quantifiers. That has been known to have extremely bad performance
+// problems on some browsers for very long strings. A PATH is expected to be
+// reasonably short. A PATH is allowed to belong to a very restricted subset of
+// Goessner's JSONPath.
+
+// So,
+//      var s = '[{"$ref":"$"}]';
+//      return JSON.retrocycle(JSON.parse(s));
+// produces an array containing a single element which is the array itself.
+
+        var px =
+/^\$(?:\[(?:\d?|\"(?:[^\\\"\u0000-\u001f]|\\([\\\"\/bfnrt]|u[0-9a-zA-Z]{4}))*\")\])*$/;
+
+        (function rez(value) {
+
+// The rez function walks recursively through the object looking for $ref
+// properties. When it finds one that has a value that is a path, then it
+// replaces the $ref object with a reference to the value that is found by
+// the path.
+
+            var i, item, name, path;
+
+            if (value && typeof value === 'object') {
+                if (Object.prototype.toString.apply(value) === '[object Array]') {
+                    for (i = 0; i < value.length; i += 1) {
+                        item = value[i];
+                        if (item && typeof item === 'object') {
+                            path = item.$ref;
+                            if (typeof path === 'string' && px.test(path)) {
+                                value[i] = eval(path);
+                            } else {
+                                rez(item);
+                            }
+                        }
+                    }
+                } else {
+                    for (name in value) {
+                        item = value[name];
+                        if (item && typeof item === 'object') {
+                            path = item.$ref;
+                            if (typeof path === 'string' && px.test(path)) {
+                                value[name] = eval(path);
+                            } else {
+                                rez(item);
+                            }
+                        }
+                    }
+                }
+            }
+        }($));
+        return $;
+    };
+}