CODEWITHSUNDEEP
javascriptregex
Bookin
Bookin

Reputation: 282

JS Regexp - how to find text in a string

There is some text, exp: "The string class is an instantiation of the basic_string class template that uses char".

I need to find the text - "basic_string", but if there is no word "the" in front of him.

If use negative lookbehind, it was be:

(?<!\sthe)\s+basic_string

But javascript not understand negative lookbehind, what to do?

Upvotes: 3

Views: 167

Answers (4)

Wiktor Stribiżew
Wiktor Stribiżew

Reputation: 627244

The easiest way to emulate the negative lookbehind is via an optional capturing group, and check if the group participated in the match:

/(\bthe)?\s+basic_string/g
 ^^^^^^^^

See this JS demo:

var s = 'The string class is an instantiation of the basic_string class template that uses char, not basic_string.';
var re = /(\bthe)?(\s+basic_string)/gi;
var res = s.replace(re, function(match, group1, group2) {
   return group1 ? match : "<b>" + group2 + "</b>";
});
document.body.innerHTML = res;

Upvotes: 1

guest271314
guest271314

Reputation: 1

You can use RegExp /(the)(?\sbasic_string)/ or new RegExp("(" + before + ")(?=" + match + ")") to match "the" if followed by " basic_string", .match() to retrieve .index of matched string, .slice() to get "basic_string"

var str = "The string class is an instantiation of the basic_string class template that uses char";
var before = "the";
var match = " basic_string";
var index = str.match(new RegExp("(" + before + ")(?=" + match + ")")).index 
            + before.length + 1;
console.log(str.slice(index, index + match.length));

Upvotes: 1

logi-kal
logi-kal

Reputation: 7880

If the only allowed character between "the" and "basic_string" is the white-space:

([^e\s]|[^h]e|[^t]he)\s+basic_string

Upvotes: 3

anubhava
anubhava

Reputation: 785731

You can use xregexp library to get advanced regex features like lookbehind in Javascript.

Alternatively you can use alternation and capture group as a workaround:

var s = 'The string class is an instantiation of the basic_string class template that uses char';

var kw = s.match(/\bthe basic_string\b|(\bbasic_string\b)/)[1];
// undefined

s = 'instantiation of basic_string class template'
kw = s.match(/\bthe basic_string\b|(\bbasic_string\b)/)[1]
//=> "basic_string"

In this regex, captured group #1 will only be populated if bbasic_string isn't preceded by word the.

Upvotes: 1

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