Javascript regex replace with conditions

Question

I want to use regex in JavaScript to replace some words in a multi-line text. Origin:

Doka (1) is 20 years old. Doka, (2) Sole are my friends. Sole told me "Doka (3) is a nice gỉrl!"
Doka: (4) student of Hamma school.
I met Doka (5) yesterday.

Result of replacement as expected:

Bob (1) is 20 years old. Bob, (2) Sole are my friends. Sole told me "Doka (3) is a nice gỉrl!"
Doka: (4) student of Hamma school.
I met Bob (5) yesterday.

In this example, I would want to replace Doka (1, 2, 5) with Bob. The conditions to replace a match are:

Not inside double quotes.
Not between a carriage return and a colon.

How can I do that?

trincot · Accepted Answer · 2016-12-11 00:18:18Z

2

You could use this regular expression and code, provided that any double quotes are properly closed, i.e. they occur an even number of times:

var str = `Doka (1) is 20 years old. Doka, (2) Sole are my friends. Sole told me "Doka (3) is a nice gỉrl!"
Doka: (4) student of Hamma school.
I met Doka (5) yesterday.`;

str = str.replace(/(([^\n\r])Doka|Doka(?!:))(?=([^"]*"[^"]*")*[^"]*$)/g, '$2Bob');

console.log(str);

Explanation:

([^\n\r])Doka: matches "Doka" and the character preceding it, provided that this preceding character is not a line-break character (i.e. neither a linefeed nor a carriage return). That character is captured in a group (parentheses), so we can restore it during the replacement.
|Doka(?!:): in case the above does not match this alternative will be tried. This happens when there is not any preceding character (i.e. "Doka" appears at the very start), or a line-break character precedes it. In this case we only allow a match when "Doka" is not followed by a colon.

The above two expressions are put in another set of parentheses to set the boundary of the OR (|) operation. This becomes the first capture group.

(?=([^"]*"[^"]*")*[^"]*$): this requires that a potential match is followed by an even number of quotes up to the very end ($) of the string. This comes down to requiring that the match is not wrapped in double quotes.

The replacement string $2Bob restores the second capture group (which is what is matched by [^\n\r], and could be nothing at all), and then inserts "Bob".

edited Dec 11, 2016 at 0:18

answered Dec 11, 2016 at 0:07

trincot

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3 Comments

trincot Over a year ago

@qxz, I have added some explanation.

user3120188 Over a year ago

Preceding character is not a dot. How to solve this?

trincot Over a year ago

You want to not replace when there is a dot before the word? That is exactly the same requirement as that there can be no newline before it, so just add that character to the list, like [^\n\r.]. Do you understand this notation? [^ .... ]? You can read about regular expressions here.

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