ltgt

implement correct ranges for level-*


example

`` js
var ltgt = require('ltgt')

ltgt.start(range) //the start of the range
ltgt.end(range) //the end of the range

//returns the lower/upper bound, whether it's inclusive or not.
ltgt.lowerBound(range)
ltgt.upperBound(range)

ltgt.lt(range)
ltgt.gt(range)
ltgt.lte(range)
ltgt.gte(range)

//return wether this is a reversed order
//(this is significant for start/end ranges
ltgt.reverse(range)
var filter = ltgt.filter(range)

filter(key) == true //if key contained in range.

ltgt.contains(range, key)

`

ways to specify ranges

there have been a variety of ways to specify ranges in level-*.
this module supports them all.

gt/gte, lt/lte

specify a range between a lower bound (gt, gte) and an upper bound (lt, lte)

if gte and gt is undefined, read from the start of the database,
if lte and lt is undefined, read until the end of the database,

min, max

legacy level-sublevel style,
synonym for gte, lte.

start, end, reverse

legacy levelup style.

The range is from start -> end, start does not specify the lowest
record, instead it specifies the first record to be read. However,
reverse must also be passed correctly. This is way to specify a range is
confusing if you need to read in reverse,
so it's strongly recommended to use gt/gte,lt/lte.

If reverse is true,
start must be undefined or less than end,
unless end is undefined.

if reverse is false
end must be undefined or greater than start,
unless start is undefined.

if start is undefined, read from the first record in the database
if end is undefined read until the last record in the database.

api

ltgt.contains(range, key, compare)

using the provided compare method, return true if key
is within range. compare defaults to ltgt.compare

ltgt.filter(range, compare)

return a function that returns true if it's argument is within range.
can be passed to Array.filter

` js
[1,2,3,4,5].filter(ltgt.filter({gt: 2, lte: 4})
// => [3, 4]
`

ltgt.lowerBound(range)

return the lower bound of range.
Incase the lower bound is specified with gt,
check ltgt.lowerBoundExclusive

ltgt.upperBound(range)

return the upperBound of range.
Incase the upper bound is specified with gt,
check ltgt.upperBoundExclusive

ltgt.lowerBoundExclusive(range)

return true if upper bound is exclusive.

ltgt.upperBoundExclusive(range)

return true if lower bound is exclusive.

ltgt.start(range, default)

The start of the range. This takes into account direction (reverse)
If a start is not provided, default is used.

ltgt.end(range, default)

The end of the range. This takes into account direction (reverse)
If a end is not provided, default is used.

ltgt.startInclusive(range)

returns true if the range should start at the exact value returned
by start(range) otherwise, it should skip one input.

ltgt.endInclusive(range)

returns true if the range should include the exact value returned
by end(range) otherwise, it should end on that value.

ltgt.toLtgt(range, _range, map, lowerBound, upperBound)

convert a range to a new ltgt range. _range
is the object to return - if you want to mutate range
call ltgt.toLtgt(range, range, map)

map gets called on each key in the range, and wether it's an upper or lower bound -
so can be used as an encode function.

map(value, isUpperBound) if isUpperBound` is false, this is the lower bound.

License

MIT