javascript - Regex test function do not return the same depending quotes -

i have weird case regular expression in javascript:

var re = /[^\s]+(?:\s+|$)/g; re.test('foo'); // return true re.test("foo"); // return false 

is regular expression type sensitive? first goal extract word (separated 1 or more whitespace) of string.

thanks help.

julien

when using g flag on javascript regular expression, keep track of last match found , start searching index next time try find match.

between 2 re.test() calls, take @ re.lastindex see talking about.

for example:

var re = /[^\s]+(?:\s+|$)/g; re.test('foo'); // return true re.lastindex;   // 3 re.test("foo"); // return false 

you notice type of quotes use not matter, re.test('foo'); re.test('foo'); have same behavior.

if want regex start fresh, can either remove global flag regex or set re.lastindex 0 after each attempt find match, example:

var re = /[^\s]+(?:\s+|$)/g; re.test('foo'); // return true re.lastindex = 0; re.test("foo"); // return true 

the alternating noted blender in comments can explained because lastindex automatically set 0 when match fails, next attempt after failure succeed.