Check if a string starts with http using Javascript

问题

I've been searching all over for an answer to this and all of the answers I've found haven't been in JavaScript.

I need a way, in javascript, to check if a string starts with http, https, or ftp. If it doesn't start with one of those I need to prepend the string with http://. indexOf won't work for me I don't think as I need either http, https or ftp. Also I don't want something like google.com/?q=http://google.com to trigger that as being valid as it doesn't start with an http whereas indexOf would trigger that as being true (if I'm not entirely mistaken).

The closest PHP regex I've found is this:

function addhttp($url) {
   if (!preg_match("~^(?:f|ht)tps?://~i", $url)) {
      $url = "http://" . $url;
   }
   return $url;
}

Source: How to add http if its not exists in the url

I just don't know how to convert that to javascript. Any help would be greatly appreciated.

回答1:

export const getValidUrl = (url = "") => {
    let newUrl = window.decodeURIComponent(url);
    newUrl = newUrl.trim().replace(/\s/g, "");

    if(/^(:\/\/)/.test(newUrl)){
        return `http${newUrl}`;
    }
    if(!/^(f|ht)tps?:\/\//i.test(newUrl)){
        return `http://${newUrl}`;
    }

    return newUrl;
};

Tests:

expect(getValidUrl('https://www.test.com')).toBe('https://www.test.com');
expect(getValidUrl('http://www.test.com')).toBe('http://www.test.com');
expect(getValidUrl('    http   :    /  /  www.test.com')).toBe('http://www.test.com');
expect(getValidUrl('ftp://www.test.com')).toBe('ftp://www.test.com');
expect(getValidUrl('www.test.com')).toBe('http://www.test.com');
expect(getValidUrl('://www.test.com')).toBe('http://www.test.com');
expect(getValidUrl('http%3A%2F%2Fwww.test.com')).toBe('http://www.test.com');
expect(getValidUrl('www    .  test.com')).toBe('http://www.test.com');

回答2:

This should work:

var pattern = /^((http|https|ftp):\/\/)/;

if(!pattern.test(url)) {
    url = "http://" + url;
}

jsFiddle

回答3:

var url = "http://something.com"
if( url.indexOf("http") == 0 ) {
    alert("yeah!");
} else {
    alert("No no no!");
}

回答4:

This should work:

var re = /^(http|https|ftp)/

回答5:

Non-Regex declarative way:

export const hasValidUrlProtocol = (url = '') => 
    Boolean(['http://', 'https://', 'ftp://'].some(protocol => url.startsWith(protocol)))

回答6:

Refining previous answers a bit more, I used new RegExp(...) to avoid messy escapes, and also added an optional s.

var pattern = new RegExp('^(https?|ftp)://');

if(!pattern.test(url)) {
    url = "http://" + url;
}

var pattern = new RegExp('^(https?|ftp)://');


console.log(pattern.test('http://foo'));
console.log(pattern.test('https://foo'));
console.log(pattern.test('ftp://foo'));
console.log(pattern.test('bar'));

来源：https://stackoverflow.com/questions/11300906/check-if-a-string-starts-with-http-using-javascript

标签

javascript

regex