Javascript: recursively encode and decode querystring. (object to querystring, querystring to object)

Question

I want to encode a complex json/javascript object into the standard querystring encoding. And i want to decode this querystring back to an json/javascript object. It should be recursively, with arrays, objects, strings, booleans and numbers.

I thought this should be easy, but was proven wrong. Does anyone have an idea, how to solve this problem? Either in Javascript or preferably in Typescript.

Answer 1

I think, what you want to do, is encode and decode nested objects.

There is no single standard, but very often, QS (Query String) syntax is used:

{
    "attribute": "value",
    "array": ["apples", "bananas"],
    "object": { "number": 55 },
}

will become:

?attribute=value&array[0]=apples&array[1]=bananas&object[number]=55

Example code:

function decode(querystring: string): object {
    function parseValue(value: string): any {
        if (value === 'TRUE') return true;
        if (value === 'FALSE') return false;
        return isNaN(Number(value)) ? value : Number(value);
    }

    function dec(list: any[], isArray = false): object {
        let obj: any = isArray ? [] : {};

        let recs: any[] = list.filter((item) => {
            if (item.keys.length > 1) return true;
            obj[item.keys[0]] = parseValue(item.value);
        });

        let attrs = {};
        recs.map((item) => {
            item.key = item.keys.shift();
            attrs[item.key] = [];
            return item;
        }).forEach((item) => attrs[item.key].push(item));

        Object.keys(attrs).forEach((attr) => {
            let nextKey = attrs[attr][0].keys[0];
            obj[attr] = dec(attrs[attr], typeof nextKey === 'number');
        });

        return obj;
    }

    return dec(
        querystring
            .split('&')
            .map((item) => item.split('=').map((x) => decodeURIComponent(x)))
            .map((item) => {
                return {
                    keys: item[0]
                        .split(/[\[\]]/g)
                        .filter((n) => n)
                        .map((key) => (isNaN(Number(key)) ? key : Number(key))),
                    value: item[1],
                };
            })
    );
}

export function encode(object: object): string {
    function reducer(obj, parentPrefix = null) {
        return function (prev, key) {
            const val = obj[key];
            key = encodeURIComponent(key);
            const prefix = parentPrefix ? `${parentPrefix}[${key}]` : key;

            if (val == null || typeof val === 'function') {
                prev.push(`${prefix}=`);
                return prev;
            }

            if (typeof val === 'boolean') {
                prev.push(`${prefix}=${val.toString().toUpperCase()}`);
                return prev;
            }

            if (['number', 'string'].includes(typeof val)) {
                prev.push(`${prefix}=${encodeURIComponent(val)}`);
                return prev;
            }

            prev.push(
                Object.keys(val).reduce(reducer(val, prefix), []).join('&')
            );
            return prev;
        };
    }

    return Object.keys(object).reduce(reducer(object), []).join('&');
}