This API is available on Firefox OS for internal applications 仅。
getLength()
方法在
DataStore
interface returns the number of records stored in the current data store.
注意 : The Data Store API is available in Web 工作者 , from Firefox 32 onwards (Firefox OS 2.0; see bug 949325 )。
store.getLength().then(function(storeLength) {
// Do something with storeLength
});
A
Promise
object of type unsigned long that resolves with a numeric variable containing the number of records stored in the current data store.
In the following example, we use
navigator.getDataStores
to return a list of
DataStore
objects representing data stores on the device called
contacts
. Since there is only one such data store, we can access it inside the outer promise using
stores[0]
. The next promise uses
DataStore.getLength
to return the number of records in the store. If the value is 0, we populate the data store with records contained in the
contactsInit
object; if there is already data in the store, we run
DataStore.sync
to loop through any additions since the code last accessed the data store and update the data display as necessary.
navigator.getDataStores('contacts').then(function(stores) {
stores[0].getLength().then(function(storeLength) {
if(storeLength == 0) {
for(i = 0; i < contactsInit.length; i++) {
addContact(stores[0],contactsInit[i]);
};
} else {
var cursor = stores[0].sync();
runNextTask(cursor);
}
});
});
注意 : This code is taken from our Data Store Contacts Editor demo. Look through the code to help you understand better what is going on, and how the full code works.
| 规范 | 状态 | 注释 |
|---|---|---|
|
Data Store API
The definition of 'getLength()' in that specification. |
草案 |
The discussion concerning this API's creation happened in various Mozilla mailing lists and other places. A summary of the discussion and further pointers can be found on the Mozilla Wiki . For further feedback and questions, send mail to the dev-webapi mailing list.