Question

I have a searching system that splits the keyword into chunks and searches for it in a string like this:

var regexp_school = new RegExp("(?=.*" + split_keywords[0] + ")(?=.*" + split_keywords[1] + ")(?=.*" + split_keywords[2] + ").*", "i");

I would like to modify this so that so that I would only search for it in the beginning of the words.

For example if the string is:

"Bbe be eb ebb beb"

And the keyword is: "be eb"

Then I want only these to hit "be ebb eb"

In other words I want to combine the above regexp with this one:

var regexp_school = new RegExp("^" + split_keywords[0], "i");

But I’m not sure how the syntax would look like.

I’m also using the split function to split the keywords, but I don’t want to set a length since I don’t know how many words there are in the keyword string.

split_keywords = school_keyword.split(" ", 3);

If I leave the 3 out, will it have dynamic length or just length of 1? I tried doing a

 alert(split_keywords.lenght);

But didn’t get a desired response

Answer 1

You should use the special word boundary character \b to match the beginning of a word. To create the expression for an arbitrary number of keywords, you can generate it in a loop.

var regex = '';

for(var i = split_keywords.length;i--; ) {
    // two slashes are needed to insert `\` literally
    regex += "(?=.*\\b" + split_keywords[i] + ")";
}

var regexp_school = new RegExp(regex, "i");

I’m not sure about performance, but you can also consider to use indexOf to test whether a substring is contained in a string.

Update:

If \b does not work for you (because of other “special” characters), and all your words are separated by a white space, you can use

"(?=.*\\s" + split_keywords[i] + ")"

or

"(?=.* " + split_keywords[i] + ")"

But for this to work you have to prepend the text you are searching in with a white space:

" " + textYouSearchIn

or you are write a more complex expression:

"(?=(^|.*\\s)" + split_keywords[i] + ")"