Convert relative path to absolute using JavaScript

Question

There\'s a function, which gives me urls like:

./some.css
./extra/some.css
../../lib/slider/slider.css

It\'s always a relative path.

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Answer 1

The proposed and accepted solution does not support server relative URLs and does not work on absolute URLs. If my relative is /sites/folder1 it won't work for example.

Here is another function that supports full, server relative or relative URLs as well as ../ for one level up. It is not perfect but covers a lot of options. Use this when your base URL is not the current page URL, otherwise there are better alternatives.

    function relativeToAbsolute(base, relative) {
    //make sure base ends with /
    if (base[base.length - 1] != '/')
        base += '/';

    //base: https://server/relative/subfolder/
    //url: https://server
    let url = base.substr(0, base.indexOf('/', base.indexOf('//') + 2));
    //baseServerRelative: /relative/subfolder/
    let baseServerRelative = base.substr(base.indexOf('/', base.indexOf('//') + 2));
    if (relative.indexOf('/') === 0)//relative is server relative
        url += relative;
    else if (relative.indexOf("://") > 0)//relative is a full url, ignore base.
        url = relative;
    else {
        while (relative.indexOf('../') === 0) {
            //remove ../ from relative
            relative = relative.substring(3);
            //remove one part from baseServerRelative. /relative/subfolder/ -> /relative/
            if (baseServerRelative !== '/') {
                let lastPartIndex = baseServerRelative.lastIndexOf('/', baseServerRelative.length - 2);
                baseServerRelative = baseServerRelative.substring(0, lastPartIndex + 1);
            }
        }
        url += baseServerRelative + relative;//relative is a relative to base.
    }

    return url;
}

Hope this helps. It was really frustrating not to have this basic utility available in JavaScript.