How to check if a string is a valid URL slug in JavaScript?

To check if a string is a valid URL slug, we can use a regex expression to match for strings that are small English alphabets separated by a dash in JavaScript.

TL;DR

// Regular expression to check if string is a valid url slug
const regexExp = /^[a-z0-9]+(?:-[a-z0-9]+)*$/g;

// String with valid url slug
const str = "hello-world";

regexExp.test(str); // true

This is the regex expression for matching almost all the test cases for a valid URL slug in JavaScript.

// Regular expression to check if string is a valid url slug
const regexExp = /^[a-z0-9]+(?:-[a-z0-9]+)*$/g;

Now let's write a string with valid URL slug like this,

// Regular expression to check if string is a valid url slug
const regexExp = /^[a-z0-9]+(?:-[a-z0-9]+)*$/g;

// String with valid url slug
const str = "hello-world";

Now to test the string, we can use the test() method available in the regular expression we defined. It can be done like this,

// Regular expression to check if string is a valid url slug
const regexExp = /^[a-z0-9]+(?:-[a-z0-9]+)*$/g;

// String with valid url slug
const str = "hello-world";

regexExp.test(str); // true

The test() method will accept a string type as an argument to test for a match.
The method will return boolean true if there is a match using the regular expression and false if not.

See the above example live in JSBin.

If you want this as a utility function which you can reuse, here it is,

/* Check if string is a valid URL slug */
function checkIfValidURLSlug(str) {
  // Regular expression to check if string is a valid url slug
  const regexExp = /^[a-z0-9]+(?:-[a-z0-9]+)*$/g;

  return regexExp.test(str);
}

// Use the function
checkIfValidURLSlug("hello-world"); // true
checkIfValidURLSlug("HELLO-world"); // false