static mergeItem(key, value, callback?)
Merges existing value with input value, assuming they are stringified json. Returns a Promise object. Not supported by all native implementations.
Example:
let UID123_object = {
name: 'Chris',
age: 30,
traits: {hair: 'brown', eyes: 'brown'},
};
// need only define what will be added or updated
let UID123_delta = {
age: 31,
traits: {eyes: 'blue', shoe_size: 10}
};
AsyncStorage.setItem('UID123', JSON.stringify(UID123_object), () => {
AsyncSto