RegExp: lastIndex
lastIndex
is a read/write integer property of RegExp
instances that specifies the index at which to start the next match.
Note that lastIndex
is not a property of the RegExp
prototype but is instead only exposed from RegExp
instances.
Property attributes of RegExp: lastIndex |
|
---|---|
Writable | yes |
Enumerable | no |
Configurable | no |
Description
This property is set only if the regular expression instance used the g
flag to indicate a global search, or the y
flag to indicate a sticky search. The following rules apply when test()
and exec()
are called on a given input:
- If
lastIndex
is greater than the length of the input,exec()
ortest()
will not find a match, andlastIndex
will be set to 0. - If
lastIndex
is equal to or less than the length of the input,exec()
ortest()
will attempt to match the input starting fromlastIndex
.- If
exec()
ortest()
find a match, thenlastIndex
will be set to the position of the end of the matched string in the input. - If
exec()
ortest()
do not find a match, thenlastIndex
will be set to 0.
- If
Examples
Using lastIndex
Consider the following sequence of statements:
var re = /(hi)?/g;
Matches the empty string.
console.log(re.exec('hi'));
console.log(re.lastIndex);
Returns ["hi", "hi"]
with lastIndex
equal to 2.
console.log(re.exec('hi'));
console.log(re.lastIndex);
Returns ["", undefined]
, an empty array whose zeroth element is the match string. In this case, the empty string because lastIndex
was 2 (and still is 2) and hi
has length 2.
Specifications
Specification |
---|
ECMAScript Language Specification # sec-properties-of-regexp-instances |
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