Bug 103822 – RegExp.prototype.exec should always update lastIndex if no match was found

• Status: UNCONFIRMED
• Component: JavaScriptCore

[André Bargull]

Steps to reproduce:

Simple test case:
---
js> r = /a/; r.lastIndex = 1; r.exec("zzzz"); r.lastIndex
1
---


Actual results:

`r.lastIndex` should have been set to `0` per ES5.1, cf. [15.10.6.2 RegExp.prototype.exec(string) - step 9a].

Spidermonkey and V8 also return `1` whereas IE10 and Opera12 return `0`.

[André Bargull]

RegExp.prototype.test, String.prototype.match and String.prototype.replace are also affected.
List of different javascript engines/browsers and the result for each test:
---
r = /a/; r.lastIndex = 1; r.exec("zzzz"); r.lastIndex
Bad: JSC, V8, SM
Good: Opera, IE

r = /a/; r.lastIndex = 1; r.test("zzzz"); r.lastIndex
Bad: JSC, V8, SM, Opera
Good: IE

r = /a/; r.lastIndex = 1; "zzzz".match(r); r.lastIndex
Bad: JSC, V8, SM
Good: Opera, IE

r = /a/; r.lastIndex = 1; "zzzz".replace(r, ""); r.lastIndex
Bad: JSC, V8, SM, Opera
Good: IE
---