source: node_modules/json-stable-stringify/index.js

'use strict';

var jsonStringify = (typeof JSON !== 'undefined' ? JSON : require('jsonify')).stringify;

var isArray = require('isarray');
var objectKeys = require('object-keys');
var callBind = require('call-bind');
var callBound = require('call-bind/callBound');

var $join = callBound('Array.prototype.join');
var $push = callBound('Array.prototype.push');

var strRepeat = function repeat(n, char) {
        var str = '';
        for (var i = 0; i < n; i += 1) {
                str += char;
        }
        return str;
};

var defaultReplacer = function (parent, key, value) { return value; };

module.exports = function stableStringify(obj) {
        var opts = arguments.length > 1 ? arguments[1] : void undefined;
        var space = (opts && opts.space) || '';
        if (typeof space === 'number') { space = strRepeat(space, ' '); }
        var cycles = !!opts && typeof opts.cycles === 'boolean' && opts.cycles;
        var replacer = opts && opts.replacer ? callBind(opts.replacer) : defaultReplacer;

        var cmpOpt = typeof opts === 'function' ? opts : opts && opts.cmp;
        var cmp = cmpOpt && function (node) {
                var get = cmpOpt.length > 2 && function get(k) { return node[k]; };
                return function (a, b) {
                        return cmpOpt(
                                { key: a, value: node[a] },
                                { key: b, value: node[b] },
                                get ? { __proto__: null, get: get } : void undefined
                        );
                };
        };

        var seen = [];
        return (function stringify(parent, key, node, level) {
                var indent = space ? '\n' + strRepeat(level, space) : '';
                var colonSeparator = space ? ': ' : ':';

                if (node && node.toJSON && typeof node.toJSON === 'function') {
                        node = node.toJSON();
                }

                node = replacer(parent, key, node);

                if (node === undefined) {
                        return;
                }
                if (typeof node !== 'object' || node === null) {
                        return jsonStringify(node);
                }
                if (isArray(node)) {
                        var out = [];
                        for (var i = 0; i < node.length; i++) {
                                var item = stringify(node, i, node[i], level + 1) || jsonStringify(null);
                                $push(out, indent + space + item);
                        }
                        return '[' + $join(out, ',') + indent + ']';
                }

                if (seen.indexOf(node) !== -1) {
                        if (cycles) { return jsonStringify('__cycle__'); }
                        throw new TypeError('Converting circular structure to JSON');
                } else { $push(seen, node); }

                var keys = objectKeys(node).sort(cmp && cmp(node));
                var out = [];
                for (var i = 0; i < keys.length; i++) {
                        var key = keys[i];
                        var value = stringify(node, key, node[key], level + 1);

                        if (!value) { continue; }

                        var keyValue = jsonStringify(key)
                                + colonSeparator
                                + value;

                        $push(out, indent + space + keyValue);
                }
                seen.splice(seen.indexOf(node), 1);
                return '{' + $join(out, ',') + indent + '}';

        }({ '': obj }, '', obj, 0));
};