// set data in database
        setData('/users/john', { name: 'john', age: 37 })
        .then(res => {
             console.log(res);
        })
        .catch(err => console.log(err))

        // update data in database
        updateData('/users/john', { age: 39 })
        .then(res => {
            console.log(res);
        })
        .catch(err => console.log(err))  

        // remove data from database
        removeData('/users/john')
        .then(res => {
            console.log(res);
        })
        .catch(err => console.log(err))