IDBKeyRange.lower - Web APIs 编辑

The lower read-only property of the IDBKeyRange interface returns the lower bound of the key range.

Note:

Syntax

var lower = myKeyRange.lower

Value

The lower bound of the key range (can be any type.)

Example

The following example illustrates how you'd use a key range. Here we declare keyRangeValue = IDBKeyRange.upperBound("F", "W", true, true); — a range that includes everything between "F" and "W" but not including them — since both the upper and lower bounds have been declared as open (true). We open a transaction (using IDBTransaction) and an object store, and open a Cursor with IDBObjectStore.openCursor, declaring keyRangeValue as its optional key range value.

After declaring the key range, we log its lower property value to the console, which should appear as "F".

Note: For a more complete example allowing you to experiment with key range, have a look at our IDBKeyRange-example repo (view the example live too.)

function displayData() {
  var keyRangeValue = IDBKeyRange.bound("F", "W", true, true);
  console.log(keyRangeValue.lower);

  var transaction = db.transaction(['fThings'], 'readonly');
  var objectStore = transaction.objectStore('fThings');

  objectStore.openCursor(keyRangeValue).onsuccess = function(event) {
    var cursor = event.target.result;
      if(cursor) {
        var listItem = document.createElement('li');
        listItem.innerHTML = '<strong>' + cursor.value.fThing + '</strong>, ' + cursor.value.fRating;
        list.appendChild(listItem);

        cursor.continue();
      } else {
        console.log('Entries all displayed.');
      }
    };
  };

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• Using IndexedDB
• Starting transactions: IDBDatabase
• Using transactions: IDBTransaction
• Setting a range of keys: IDBKeyRange
• Retrieving and making changes to your data: IDBObjectStore
• Using cursors: IDBCursor
• Reference example: To-do Notifications (view example live.)