Skip to main content

class Storage.Index

Index object in persistent storage.

Indexes are by themselves persistable collections:

storage.root = {
  version:1,
  notes: storage.createIndex("string") // note by id (string, GUID) index
}

Properties​

length​

integer, read-only, length of an index, number of items (objects) in the index.

unique​

boolean, read-only, true if the index was declared as unique.

type​

string, read-only, key type as it was declared at creation time. Read-only property.

Enumeration​

Indexes support for(of) enumeration style:

// log all objects in the index 
for( let obj of index ) 
  console.log(obj);

Order of enumeration is ascending.

tip

To enumarate index items in descending order use index.select().

Methods​

set()​

index.set( key, obj [, replace: true|false ] ) : true|false

Inserts obj object into the index and associates it with the key value. Optionally, in-case of non-unique index, replaces it with existing object if such key is already present in the index and replace is true.

get()​

index.get( key ) returns: object | [objects...]

Returns object at the key position or null. key has to be of the same type as the type of the index object. If the index was created as non unique then the return value is an array - list of items under the key (array can be empty if no items under such key).

delete()​

index.delete( key [,obj] ) returns: true | false

Method removes object obj by key from the index. Method returns true on success, otherwise false. If the index is unique, obj is optional.

select()​

index.select( minKey, maxKey [, ascending [, startInclusive [, endInclusive]]] ) returns: Iterator.

returns selection in the Index based on min-key/ max-key criteria , ascent or descent order, start-inclusive, end-inclusive.

parameters:

  • minKey, maxKey - of index type, min/max values of key to select;
  • ascending - boolean, true if to enumerate items in ascending order, false - in descending. Default value ascending:true.
  • startInclusive, endInclusive - boolean, true if start/end of enumeration shall include minKey/maxKey themselves.

This method is intended to be used in for(of) enumerations:

for( const obj in index.select(minVal, maxVal) ) { 
 ... 
}
tip

minKey or maxKey can be null - means search from very first or very last key in the index.

clear()​

index.clear()

Removes all items from the index object - makes it empty.