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95 lines
3.5 KiB
95 lines
3.5 KiB
3 years ago
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# Flatted Specifications
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This document describes operations performed to produce, or parse, the flatted output.
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## stringify(any) => flattedString
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The output is always an `Array` that contains at index `0` the given value.
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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`.
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In case it's an `Array`, an `Object`, or a `string`, return the index as `string`, associated through a `Map`.
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Giving the following example:
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```js
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flatted.stringify('a'); // ["a"]
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flatted.stringify(['a']); // [["1"],"a"]
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flatted.stringify(['a', 1, 'b']); // [["1",1,"2"],"a","b"]
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```
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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"]`.
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The exact same happens for objects.
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```js
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flatted.stringify('a'); // ["a"]
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flatted.stringify({a: 'a'}); // [{"a":"1"},"a"]
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flatted.stringify({a: 'a', n: 1, b: 'b'}); // [{"a":"1","n":1,"b":"2"},"a","b"]
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```
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Every object, string, or array, encountered during serialization will be stored once as stringified index.
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```js
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// per each property/value of the object/array
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if (any == null || !/object|string/.test(typeof any))
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return any;
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if (!map.has(any)) {
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const index = String(arr.length);
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arr.push(any);
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map.set(any, index);
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}
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return map.get(any);
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```
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This, performed before going through all properties, grants unique indexes per reference.
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The stringified indexes ensure there won't be conflicts with regularly stored numbers.
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## parse(flattedString) => any
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Everything that is a `string` is wrapped as `new String`, but strings in the array, from index `1` on, is kept as regular `string`.
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```js
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const input = JSON.parse('[{"a":"1"},"b"]', Strings).map(strings);
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// convert strings primitives into String instances
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function Strings(key, value) {
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return typeof value === 'string' ? new String(value) : value;
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}
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// converts String instances into strings primitives
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function strings(value) {
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return value instanceof String ? String(value) : value;
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}
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```
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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.
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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.
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If such `value` is an object and it hasn't been parsed yet, add it as parsed and go through all its properties/values.
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```js
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// outside any loop ...
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const parsed = new Set;
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// ... per each property/value ...
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if (value instanceof Primitive) {
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const tmp = input[parseInt(value)];
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if (typeof tmp === 'object' && !parsed.has(tmp)) {
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parsed.add(tmp);
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output[key] = tmp;
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if (typeof tmp === 'object' && tmp != null) {
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// perform this same logic per
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// each nested property/value ...
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}
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} else {
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output[key] = tmp;
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}
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} else
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output[key] = tmp;
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```
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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.
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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.
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