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?
If the only allowed character between "the" and "basic_string" is the white-space:
([^e\s]|[^h]e|[^t]he)\s+basic_string
(^|[^e\s]|(^|[^h])e|(^|[^t])he|\wthe)\s+basic_string covers even those particular cases.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.
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));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;