Prepending "http://" to a URL that doesn't already contain "http://"

Question

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?

score 118 · Answer 1 · answered Aug 22 '10 at 20:31

118

If you also want to allow "https://", I would use a regular expression like this:

if (!/^https?:\/\//i.test(url)) {
    url = 'http://' + url;
}

If you're not familiar with regular expressions, here's what each part means.

^ - Only match at the beginning of the string
http - Match the literal string "http"
s? - Optionally match an "s"
: - Match a colon
\/\/ - Escape the "/" characters since they mark the beginning/end of the regular expression
The "i" after the regular expression makes it case-insensitive so it will match "HTTP://", etc.

answered Aug 22 '10 at 20:31

Matthew Crumley

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You should be aware that ```!/^https?:\/\//i.test(undefined)``` is ```true```. I suggest to check if ```url``` is not falsey: ```if (!!url && !/^https?:\/\//i.test(url)) {...``` – Nikita Hismatov May 12 '17 at 07:14
4

Use ```!/^(https?:)?\/\//i.test(url)``` to handle //:example.com as well. – Akshay Goyal Jun 12 '17 at 09:47
1

With the regex in your answer, it's possible to write a one-liner: 'stackoverflow.com'.replace(/^(https?:\/\/)?/i, (a)=>a || 'http://') – brunettdan Oct 14 '19 at 08:28
How can we make it avoid FTP urls? – Amante Ninja Jun 23 '20 at 10:29

score 79 · Accepted Answer · edited May 23 '17 at 12:02

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;
}

Related questions

Note for protocol relative URLS (urls that start with) `//`, this may have unexpected results. ex: `//example.com/foo`, the code above would change it to `http:////example.com/foo` — Kevin Wheeler, Jun 24 '15 at 20:05

score 37 · Answer 3 · edited Jun 20 '20 at 09:12

Lifted from the Linkenizer (Null won't mind)

link = (link.indexOf('://') === -1) ? 'http://' + link : link;

This will prepend 'http://' to link if it can't find the :// indicating protocol. This won't work well if :// occurs elsewhere in the string, but it's good enough.

Examples:

http://www.google.com -> http://www.google.com
ftp://google.com      -> ftp://google.com
www.google.com        -> http://www.google.com
google.com            -> http://google.com

Since you said you are saving this URL, it would be a better idea to do this on the server-side, so clients who have js disabled won't mess up the links.

slight improvement: `((link.indexOf('://') === -1) && (link.indexOf('mailto:') === -1) ) ? 'http://' + link : link` — Prashant, May 17 '19 at 12:58

score 23 · Answer 4 · answered Nov 08 '18 at 11:06

23

ES6, one liner

Here is a "modern" approach:

const withHttp = url => !/^https?:\/\//i.test(url) ? `http://${url}` : url;

You can now use withHttp as a function:

const myUrl = withHttp("www.example.org");

answered Nov 08 '18 at 11:06

rap-2-h

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score 7 · Answer 5 · answered Dec 22 '15 at 08:47

7

Here is what I use for instant gratification. utilizing the keyup listener in jquery.

$('#url').keyup(function () {
        if (  ($(this).val().length >=5) && ($(this).val().substr(0, 5) != 'http:') && ($(this).val().substr(0, 5) != 'https') ) {
            $(this).val('http://' + $(this).val());
        }
    });

answered Dec 22 '15 at 08:47

cjpetrus

71
1
1

1

thanks, used this, just changed the JQuery selector to ```$('input[type=url]')``` – Dirk Jan 29 '16 at 13:14

Chango · Answer 6 · 2020-05-21T12:15:08.300

7

ES6, one liner

const withHttp = (url) => url.replace(/^(?:(.*:)?\/\/)?(.*)/i, (match, schemma, nonSchemmaUrl) => schemma ? match : `http://${nonSchemmaUrl}`);

Tested for (all return http://www.google.com):

www.google.com
google.com
//google.com
http://www.google.com
https://www.google.com
ftp://www.google.com

If anyone need to know how it works add a comment and I'll add an explanation.

edited May 21 '20 at 12:15

answered May 21 '20 at 12:08

Chango

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score 6 · Answer 7 · answered Jun 12 '17 at 10:19

Below code snippet checks for:

Checks if url is not blank
Removes stray blank spaces at start or end

Checks for http://example.com, https://example.com AND //example.com

if (!!url && !!url.trim()) { //Check if url is not blank
    url = url.trim(); //Removes blank spaces from start and end
    if (!/^(https?:)?\/\//i.test(url)) { //Checks for if url doesn't match either of: http://example.com, https://example.com AND //example.com
        url = 'http://' + url; //Prepend http:// to the URL
    }
} else {
    //Handle empty url
}

You shouldn't return http:// as a default, it's better to just add '//' double forward slashes. — Jimba Tamang, Mar 18 '20 at 04:15

score 5 · Answer 8 · answered Dec 05 '16 at 17:15

I altered @Mark Byers's answer to include "https://" as well.

function formatUrl(url){
    var httpString = 'http://'
        , httpsString = 'https://'
        ;

    if (url.substr(0, httpString.length) !== httpString && url.substr(0, httpsString.length) !== httpsString)
        url = httpString + url;

    return url;
}

score 2 · Answer 9 · answered Aug 22 '10 at 20:21

2

Something like this (writing by memory)?

if (url.toUpper(url.substring(0, 7) != "HTTP://")
  url = "http://" + url;

answered Aug 22 '10 at 20:21

Eugene Mayevski 'Callback

44,434
7
64
121

5

`url.substring(0, 7).toUpperCase()` – Ferdinand Beyer Aug 22 '10 at 20:43

score 2 · Answer 10 · answered Aug 22 '10 at 20:33

2

if (url.indexOf('http://') != 0)
    url = 'http://' + url;

answered Aug 22 '10 at 20:33

Casey Chu

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score 0 · Answer 11 · answered May 17 '17 at 09:19

I altered @Morgan Taylor's and @Mark Byer's answers to be case unsensitive. Works with http:// and https://

function formatUrl(url)
{
    var httpString = "http://";
    var httpsString = "https://";
    if (url.substr(0, httpString.length).toLowerCase() !== httpString && url.substr(0, httpsString.length).toLowerCase() !== httpsString)
                url = httpString + url;
    return url;
}

Satbir Kira · Answer 12 · 2015-11-18T10:09:53.347

-1

I personally use this, which is partially taken from php docs

$scheme = parse_url($link, PHP_URL_SCHEME);
if (empty($scheme)) {
    $link = 'http://' . ltrim($link, '/');
}

edited Nov 18 '15 at 10:09

answered Nov 18 '15 at 09:41

Satbir Kira

732
6
19

score -1 · Answer 13 · answered Aug 22 '10 at 20:26

-1

You can use "StartsWith" a member of System.String.

if (url.ToUpper().StartsWith("HTTP://"))
{ 

}

answered Aug 22 '10 at 20:26

Daniel James Bryars

4,191
3
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5

if (isNotC#) { return "StartWith does not exist."; } – Hello71 Aug 22 '10 at 20:28
And, I just knocked up a console app, targeting .net 3.5 and this compiles and builds fine: string url = @"http://msdn.microsoft.com/en-us/library/ms131452(v=VS.90).aspx"; if (url.ToUpper().StartsWith("HTTP://")) { Console.WriteLine("Is this c#, the method is defined in Assembly mscorlib.dll, v2.0.50727."); } – Daniel James Bryars Aug 22 '10 at 20:36
@Daniel James Bryars: It seems that "this is not C#" refers to the question, whose tags currently (rev.1) read "javascript html variables" - no C#. – Piskvor left the building Aug 22 '10 at 20:41
Late to the game, but JavaScript now has `String.startsWith()` https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/startsWith – Jimmerz28 Oct 29 '16 at 21:00

Prepending "http://" to a URL that doesn't already contain "http://"

13 Answers13

ES6, one liner

Linked