1727109 - regular expression

Status: RESOLVED DUPLICATE of bug 1609429

(DevTools :: Console, defect, P2)

Description

[telescop603]

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/92.0.4515.159 Safari/537.36

Steps to reproduce:

Good evening!

I created a regular expression with a sticky flag (should match any non-digit symbol):
let reg = /\D+/y
Then assigned it lastIndex:
reg.lastIndex = 6
And tested with this expression
reg.test('333333D')

Actual results:

It shows false

Expected results:

The result must be true because index 6 is a letter. I've tested this in Chrome and got true.

Comment 1

[André Bargull [:anba]]

This is only an issue when executing the steps in the devtools console, because the expression evaluation preview executes reg.test('333333D'), but doesn't reset reg.lastIndex. If you type reg.test('333333D') without pressing the enter-key, the preview will show the value true. When the enter-key is then pressed, the regular expression is executed another time and the result false is returned. When all steps are enclosed in a block-statement, the correct result true is returned:

{ let reg = /\D+/y; reg.lastIndex = 6; reg.test('333333D') }

Comment 2

[Julian Descottes [:jdescottes]]

Nicolas: probably should flag this expression as having side effects? Can you point to where this is handled.

Comment 3

[Nicolas Chevobbe [:nchevobbe]]

This is a known issue (see Bug 1609429)
I'm going to mark this bug as a duplicate, and we should probably disabled instant evaluation for regex as we already have bug reports about it.

Comment 4

[telescop603]

(In reply to André Bargull [:anba] from comment #1)

This is only an issue when executing the steps in the devtools console, because the expression evaluation preview executes reg.test('333333D'), but doesn't reset reg.lastIndex. If you type reg.test('333333D') without pressing the enter-key, the preview will show the value true. When the enter-key is then pressed, the regular expression is executed another time and the result false is returned. When all steps are enclosed in a block-statement, the correct result true is returned:

{ let reg = /\D+/y; reg.lastIndex = 6; reg.test('333333D') }

Huge thanks for the great explanation! Now I understand why it works like this.