JavaScript REGEX负面展望

Question

OK I processing some lines with JavaScript and wanted to use a negative look ahead to eliminate the line if it contained a particular phrase but I still seem to be grabbing the lines and regexbuddy and others show it matching and I am not sure why

^This (\w+) (\w+) was built in (\d+). (.+?).(?! This car has a salvage title.)$

So I need to grab some various second sentence values that are to varied to match thus the (.+?). what I don't want is if the line contains has the reference to the salvage title

SO

This Honda Accord was built in 1986. This car has 3 accidents. This car has a salvage title.

should not match because the negative look ahead should fail

but

This Honda Accord was built in 1986. This car has 3 accidents.

should match but I am getting matches on both. Am I just mis-understanding the negative look ahead or am I mis-formatting it?

Answer 1

 …(?! This car has a salvage title.)$ 

You've put the negative lookahead right before the end of the string. It will always not match there (ie succeed). It's a lookahead after all, not a lookbehind, and peeking behind the end of the string doesn't make sense.

You probably wanted to do this instead:

^This (\w+) (\w+) was built in (\d+)\. (?!This car has a salvage title)(.+?)\.$

Here, the (?!This car has a salvage title)(.+?) does match the sentence (precisely, at least one character) before the dot, which does not begin with the phrase "This car has a salvage title". Or, if you don't want that phrase anywhere after the first sentence, then use

^This (\w+) (\w+) was built in (\d+)\. (?!.*?This car has a salvage title)(.+?)\.$
//                                        ^^^