javascript - 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?

Answer 1

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.