CODEWITHSUNDEEP
javascriptregexcompare
sp00m
sp00m

Reputation: 48817

How to compare two regexps?

Why do

console.log(/a/ == /a/);

and

var regexp1 = /a/;
var regexp2 = /a/;
console.log(regexp1 == regexp2);

both return false?

Upvotes: 31

Views: 16597

Answers (4)

Andy Shellam
Andy Shellam

Reputation: 15535

Just a guess - but doesn't JavaScript create a RegExp object for your regex, and therefore because you have created two different objects (even though they have the same "value") they're actually different?

Upvotes: 4

gdoron
gdoron

Reputation: 150263

"Problem":

regex is an object- a reference type, so the comparsion is done by reference, and those are two different objects.

console.log(typeof /a/); // "object"

If both operands are objects, then JavaScript compares internal references which are equal when operands refer to the same object in memory.

MDN

Solution:

​var a = /a/;
var b = /a/;
console.log(​​​a.toString() === b.toString()); // true! yessss!

Live DEMO

Another "hack" to force the toString() on the regexes is:

console.log(a + "" === b + "");​

Upvotes: 15

omerkirk
omerkirk

Reputation: 2527

For primitive data types like int, string, boolean javascript knows what to compare, but for objects like date or regex that operator only looks at the place in memory, because you define your regexes independently they have two different places in memory so they are not equal.

Upvotes: 2

ioseb
ioseb

Reputation: 16951

Try this:

String(regexp1) === String(regexp2))

You are getting false because those two are different objects.

Upvotes: 58

Related Questions