Question

I want to replace a link as plain text format to html format.

But I got the issue that, I don’t know how to prepend the http:// prefix for the new replacement if in the original link does not exist.

var text        = "google.com and http://google.com";
var pattern     = /(\b((https?)\:\/\/)?[A-Za-z0-9]+\.(com|net|org))/ig;
text            = text.replace(pattern,"<a href='$1'>$1</a>");

I meant:

1. If: google.com will be replaced <a href="http://google.com">google.com</a>
2. If: http://google.com will be replaced <a href="http://google.com">http://google.com</a>

Answer 1

Use the overload of String.replace that takes a function:

var text = "google.com and http://google.com";
var pattern = /(\b((https?)\:\/\/)?[A-Za-z0-9]+\.(com|net|org))/ig;

text = text.replace(pattern, function (str, p1)
{
    var addScheme = p1.indexOf('http://') === -1
                    && p1.indexOf('https://') === -1;

    return '<a href="' + (addScheme ? 'http://' : '') + p1 + '">' + p1 + '</a>';
});

// text is:
// '<a href="http://google.com">google.com</a> and <a href="http://google.com">http://google.com</a>'