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Editorial Team
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Asked: 2026-05-16T08:51:39+00:00

I have an input field that saves a URL, I’d like this saved input

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I have an input field that saves a URL, I’d like this saved input to recognize when “Http//” is absent from the start of the variable but have no idea where to begin… is it possible to check only a portion of a string? – then have a function that will append if necessary?

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1 Answer

  1. Editorial Team

    A simple solution for what you want is the following:

    var prefix = 'http://';
if (s.substr(0, prefix.length) !== prefix)
{
    s = prefix + s;
}

    However there are a few things you should be aware of…

    The test here is case-sensitive. This means that if the string is initially Http://example.com this will change it to http://Http://example.com which is probably not what you want. You probably should also not modify any string starting with foo:// otherwise you could end up with something like http://https://example.com.

    On the other hand if you receive an input such as example.com?redirect=http://othersite.com then you probably do want to prepend http:// so just searching for :// might not be good enough for a general solution.

    Alternative approaches

    • Using a regular expression:

      if (!s.match(/^[a-zA-Z]+:\/\//))
{
    s = 'http://' + s;
}

    • Using a URI parsing library such as JS-URI.

      if (new URI(s).scheme === null)
{
    s = 'http://' + s;
}

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