Wednesday, June 12, 2024

URL.canParse


Parsing of URLs on the client side has been a common practice for two decades. The early days included using illegible regular expressions but the JavaScript specification eventually evolved into a new URL method of parsing URLs. While URL is incredibly useful when a valid URL is provided, an invalid string will throw an error — yikes! A new method, URL.canParse, will soon be available to validate URLs!

Providing a malformed URL to new URL will throw an error, so every use of new URL would need to be within a try/catch block:

// The correct, safest way
try {
  const url = new URL('https://davidwalsh.name/pornhub-interview');
} catch (e) {
  console.log("Bad URL provided!");
}

// Oops, these are problematic (mostly relative URLs)
new URL('/');
new URL('../');
new URL('/pornhub-interview');
new URL('?q=search+term');
new URL('davidwalsh.name');

// Also works
new URL('javascript:;');

As you can see, strings that would work properly with an <a> tag sometimes won’t with new URL. With URL.canParse, you can avoid the try/catch mess to determine URL validity:

// Detect problematic URLs
URL.canParse('/'); // false
URL.canParse('/pornhub-interview'); // false
URL.canParse('davidwalsh.name'); //false

// Proper usage
if (URL.canParse('https://davidwalsh.name/pornhub-interview')) {
  const parsed = new URL('https://davidwalsh.name/pornhub-interview');
}

We’ve come a long way from cryptic regexes and burner <a> elements to this URL and URL.canParse APIs. URLs represent so much more than location these days, so having a reliable API has helped web developers so much!

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