javascript regex to match double word gives different result everytime

Question

Here is the output from my browsers console. This regex checks for doubled_words, looks for occurrences of words (strings containing 1 or more letters) followed by whitespace followed by the same word.

var reg=/([A-Za-z\u00C0-\u1FFF\u2800-\uFFFD]+)\s+\1/gi;
undefined
reg.test("sdfs sdsdf")
true
reg.test("sdfs sdsdf")
false

the result is true alternate times, why is this weird behavior?

possible duplicate of [Regular Expression For Consecutive Duplicate Words](http://stackoverflow.com/questions/2823016/regular-expression-for-consecutive-duplicate-words) — Ole Spaarmann, Jun 19 '15 at 14:26

score 2 · Accepted Answer · answered Jun 19 '15 at 14:26

That behavior is due to use of global flag. Remove it

var reg=/([A-Za-z\u00C0-\u1FFF\u2800-\uFFFD]+)\s+\1/;

Using g causes regex state (lastIndex value) to be remembered across multipel calls to test or exec methods.

Check this official reference Read the Description section.

javascript regex to match double word gives different result everytime

1 Answers1