safe-json.js

let seen = new WeakMap();

function safeJson(key, value) {
    if (key.startsWith('_') || key.startsWith('$')) return;
    if (typeof value === 'function') return;

    if (typeof value === 'bigint' || typeof value === 'symbol') {
        return String(value);
    }

    if (typeof value === 'object') {
        if (value instanceof Date) {
            return value.toISOString();
        }
        if (value instanceof RegExp) {
            return value.toString();
        }
        let newValue = seen.get(value);
        if (value instanceof Set) {
            if (!Array.isArray(newValue)) {
                newValue = Array.from(value);
                newValue.$class = 'Set';
                seen.set(value, newValue);
            } else {
                newValue.length = value.size;
                let i = 0;
                for (let x of value) {
                    newValue[i] = x;
                    i++;
                }
            }
            return newValue;
        }
        if (value instanceof Map) {
            if (Object.prototype.toString.call(newValue) !== '[object Object]') {
                newValue = {};
                newValue.$class = 'Map';
                seen.set(value, newValue);
            } else {
                for (let k in newValue) {
                    if (!value.has(k)) {
                        delete newValue[k];
                    }
                }
            }
            for (let [k, v] of value) {
                newValue[k] = v;
            }
            return newValue;
        }
    }
    
    return value;
}