Javascript Regexp not returning global results

Question

It's my understanding that all three of these lines below should return an ARRAY with 2 results in it. Yet RegExp will only return 1 result no matter how many times the regex repeats in the string.

Can some one explain why? And perhaps suggest how I can get RegExp to give me global results?

//INTPUT: 
    console.log(new RegExp("New York", "gi").exec("New York New York")); 

//OUTPUT: 
["New York"]

//INTPUT: 
    console.log(new RegExp(/New York/gi).exec("New York New York"));

//OUTPUT: 
["New York"]

//INTPUT: 
    console.log("New York New York".match(/New York/gi));

//OUTPUT:
["New York", "New York"]

now what really intrigues me is that if you try (' New York New York ').match(/ New York /gi) it will bring just 1 result (as kinda expected) and I can't think of a better way to go around this (when otherwise needed) other than iterating over it! :( — cregox
– cregox, Commented Feb 19, 2017 at 15:11

Rob Fonseca-Ensor · Accepted Answer · 2009-09-01 15:05:54Z

26

your third example is the best way to get the array of matches.

RegExp.exec actually remembers its position, and returns the next result on subsequent calls:

>>> var v = /new york/gi
>>> v.exec("NEW YORK new york")
["NEW YORK"]
>>> v.exec("NEW YORK new york")
["new york"]
>>> v.exec("NEW YORK new york")
null

answered Sep 1, 2009 at 15:05

Rob Fonseca-Ensor

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2 Comments

Rob Fonseca-Ensor Over a year ago

you could leverage this to build an aray yourself, but it's easier to just call string.match

StefanHayden Over a year ago

I have an array of keywords that I'm trying to get a count of the number of occurrences in a string. what's the best way to do that?

Derek Swingley · Accepted Answer · 2009-09-01 15:31:20Z

13

This is expected, exec() returns a single match but provides more info about the match than match(). If you just want all the matches, use match(). From JavaScript: The Definitive Guide:

Recall that match() returns an array of matches when passed a global regular expresion. exec(), by contrast, always returns a single match and provides complete information about that match. When exec() is called on a regular epression that has the g flag, it sets the lastIndex property of the matched substring. When exec() is invoked a second time for the same regular expression, it begins its search at the character position indicated by the lastIndex property.

edited Sep 1, 2009 at 15:31

answered Sep 1, 2009 at 15:04

Derek Swingley

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