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# Flatted Specifications This document describes operations performed to produce, or parse, the flatted output. ## stringify(any) => flattedString The output is always an `Array` that contains at index `0` the given value. If the value is an `Array` or an `Object`, per each property value passed through the callback, return the value as is if it's not an `Array`, an `Object`, or a `string`. In case it's an `Array`, an `Object`, or a `string`, return the index as `string`, associated through a `Map`. Giving the following example: ```js flatted.stringify('a'); // ["a"] flatted.stringify(['a']); // [["1"],"a"] flatted.stringify(['a', 1, 'b']); // [["1",1,"2"],"a","b"] ``` There is an `input` containing `[array, "a", "b"]`, where the `array` has indexes `"1"` and `"2"` as strings, indexes that point respectively at `"a"` and `"b"` within the input `[array, "a", "b"]`. The exact same happens for objects. ```js flatted.stringify('a'); // ["a"] flatted.stringify({a: 'a'}); // [{"a":"1"},"a"] flatted.stringify({a: 'a', n: 1, b: 'b'}); // [{"a":"1","n":1,"b":"2"},"a","b"] ``` Every object, string, or array, encountered during serialization will be stored once as stringified index. ```js // per each property/value of the object/array if (any == null || !/object|string/.test(typeof any)) return any; if (!map.has(any)) { const index = String(arr.length); arr.push(any); map.set(any, index); } return map.get(any); ``` This, performed before going through all properties, grants unique indexes per reference. The stringified indexes ensure there won't be conflicts with regularly stored numbers. ## parse(flattedString) => any Everything that is a `string` is wrapped as `new String`, but strings in the array, from index `1` on, is kept as regular `string`. ```js const input = JSON.parse('[{"a":"1"},"b"]', Strings).map(strings); // convert strings primitives into String instances function Strings(key, value) { return typeof value === 'string' ? new String(value) : value; } // converts String instances into strings primitives function strings(value) { return value instanceof String ? String(value) : value; } ``` The `input` array will have a regular `string` at index `1`, but its object at index `0` will have an `instanceof String` as `.a` property. That is the key to place back values from the rest of the array, so that per each property of the object at index `0`, if the value is an `instanceof` String, something not serializable via JSON, it means it can be used to retrieve the position of its value from the `input` array. If such `value` is an object and it hasn't been parsed yet, add it as parsed and go through all its properties/values. ```js // outside any loop ... const parsed = new Set; // ... per each property/value ... if (value instanceof Primitive) { const tmp = input[parseInt(value)]; if (typeof tmp === 'object' && !parsed.has(tmp)) { parsed.add(tmp); output[key] = tmp; if (typeof tmp === 'object' && tmp != null) { // perform this same logic per // each nested property/value ... } } else { output[key] = tmp; } } else output[key] = tmp; ``` As summary, the whole logic is based on polluting the de-serialization with a kind of variable that is unexpected, hence secure to use as directive to retrieve an index with a value. The usage of a `Map` and a `Set` to flag known references/strings as visited/stored makes **flatted** a rock solid, fast, and compact, solution.