IDBKeyRange - Web APIs 编辑

The IDBKeyRange interface of the IndexedDB API represents a continuous interval over some data type that is used for keys. Records can be retrieved from IDBObjectStore and IDBIndex objects using keys or a range of keys. You can limit the range using lower and upper bounds. For example, you can iterate over all values of a key in the value range A–Z.

A key range can be a single value or a range with upper and lower bounds or endpoints. If the key range has both upper and lower bounds, then it is bounded; if it has no bounds, it is unbounded. A bounded key range can either be open (the endpoints are excluded) or closed (the endpoints are included). To retrieve all keys within a certain range, you can use the following code constructs:

A key is in a key range if the following conditions are true:

• The lower value of the key range is one of the following:
  • undefined
  • Less than key value
  • Equal to key value if lowerOpen is false.
• The upper value of the key range is one of the following:
  • undefined
  • Greater than key value
  • Equal to key value if upperOpen is false.

Note:

Properties

IDBKeyRange.lower Read only

Lower bound of the key range.

IDBKeyRange.upper Read only

Upper bound of the key range.

IDBKeyRange.lowerOpen Read only

Returns false if the lower-bound value is included in the key range.

IDBKeyRange.upperOpen Read only

Returns false if the upper-bound value is included in the key range.

Methods

Static methods

IDBKeyRange.bound()

Creates a new key range with upper and lower bounds.

IDBKeyRange.only()

Creates a new key range containing a single value.

IDBKeyRange.lowerBound()

Creates a new key range with only a lower bound.

IDBKeyRange.upperBound()

Creates a new upper-bound key range.

Instance methods

IDBKeyRange.includes()

Returns a boolean indicating whether a specified key is inside the key range.

Examples

The following example illustrates how you'd use a key range. Here we declare a keyRangeValue as a range between values of "A" and "F". 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. This means that the cursor will only retrieve records with keys inside that range. This range includes the values "A" and "F", as we haven't declared that they should be open  bounds. If we used IDBKeyRange.bound("A", "F", true, true);, then the range would not include "A" and "F", only the values between them.

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("A", "F");

  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.)