🖇 Infinitely generating linked list with memoisation (or an nth-generator).
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/*
cycle.js
2018-05-15
Public Domain.
NO WARRANTY EXPRESSED OR IMPLIED. USE AT YOUR OWN RISK.
This code should be minified before deployment.
See http://javascript.crockford.com/jsmin.html
USE YOUR OWN COPY. IT IS EXTREMELY UNWISE TO LOAD CODE FROM SERVERS YOU DO
NOT CONTROL.
*/
// The file uses the WeakMap feature of ES6.
/*jslint eval */
/*property
$ref, decycle, forEach, get, indexOf, isArray, keys, length, push,
retrocycle, set, stringify, test
*/
if (typeof JSON.decycle !== "function") {
JSON.decycle = function decycle(object, replacer) {
"use strict";
// Make a deep copy of an object or array, assuring that there is at most
// one instance of each object or array in the resulting structure. The
// duplicate references (which might be forming cycles) are replaced with
// an object of the form
// {"$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 '[{"$ref":"$"}]'.
// If a replacer function is provided, then it will be called for each value.
// A replacer function receives a value and returns a replacement value.
// JSONPath is used to locate the unique object. $ indicates the top level of
// the object or array. [NUMBER] or [STRING] indicates a child element or
// property.
var objects = new WeakMap(); // object to path mappings
return (function derez(value, path) {
// The derez function recurses through the object, producing the deep copy.
var old_path; // The path of an earlier occurance of value
var nu; // The new object or array
// If a replacer function was provided, then call it to get a replacement value.
if (replacer !== undefined) {
value = replacer(value);
}
// typeof null === "object", so go on if this value is really an object but not
// one of the weird builtin objects.
if (
typeof value === "object" &&
value !== null &&
!(value instanceof Boolean) &&
!(value instanceof Date) &&
!(value instanceof Number) &&
!(value instanceof RegExp) &&
!(value instanceof String)
) {
// 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 uses an
// ES6 WeakMap.
old_path = objects.get(value);
if (old_path !== undefined) {
return {
$ref: old_path
};
}
// Otherwise, accumulate the unique value and its path.
objects.set(value, path);
// If it is an array, replicate the array.
if (Array.isArray(value)) {
nu = [];
value.forEach(function (element, i) {
nu[i] = derez(element, path + "[" + i + "]");
});
} else {
// If it is an object, replicate the object.
nu = {};
Object.keys(value).forEach(function (name) {
nu[name] = derez(
value[name],
path + "[" + JSON.stringify(name) + "]"
);
});
}
return nu;
}
return value;
}(object, "$"));
};
}
if (typeof JSON.retrocycle !== "function") {
JSON.retrocycle = function retrocycle($) {
"use strict";
// Restore an object that was reduced by decycle. Members whose values are
// objects of the form
// {$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 $ref object with a reference to the value that is found by
// the path.
if (value && typeof value === "object") {
if (Array.isArray(value)) {
value.forEach(function (element, i) {
if (typeof element === "object" && element !== null) {
var path = element.$ref;
if (typeof path === "string" && px.test(path)) {
value[i] = eval(path);
} else {
rez(element);
}
}
});
} else {
Object.keys(value).forEach(function (name) {
var item = value[name];
if (typeof item === "object" && item !== null) {
var path = item.$ref;
if (typeof path === "string" && px.test(path)) {
value[name] = eval(path);
} else {
rez(item);
}
}
});
}
}
}($));
return $;
};
}
module.exports = JSON;