Web Storage with object key / value support.

json_storage.js

class JsonStorage {

    constructor(storage) {
        this.storage = storage;
    }

    clear() {
        this.storage.clear();
    }

    stringify(value) {
        return (typeof value === 'string') ? value : JSON.stringify(value);
    }

    decode(value) {
        try {
            return JSON.parse(value);
        } catch(e) {
            return value;
        }
    }

    getItem(keyName, defaultValue) {
        let result = this.storage.getItem(this.stringify(keyName));
        if (result === null) {
            return (typeof defaultValue === 'undefined') ? null : defaultValue;
        } else {
            return this.decode(result);
        }
    }

    len() {
        return this.storage.length;
    }

    key(index) {
        return this.storage.key(index);
    }

    removeItem(keyName) {
        this.storage.removeItem(this.stringify(keyName));
    }

    setItem(keyName, keyValue) {
        this.storage.setItem(
            this.stringify(keyName),
            this.stringify(keyValue)
        );
    }

}