freeCodeCamp/curriculum/challenges/chinese/02-javascript-algorithms-and-data-structures/functional-programming/apply-functional-programming-to-convert-strings-to-url-slugs.md

---
id: 587d7dab367417b2b2512b6d
title: Apply Functional Programming to Convert Strings to URL Slugs
challengeType: 1
forumTopicId: 301227
dashedName: apply-functional-programming-to-convert-strings-to-url-slugs
---

# --description--

The last several challenges covered a number of useful array and string methods that follow functional programming principles. We've also learned about `reduce`, which is a powerful method used to reduce problems to simpler forms. From computing averages to sorting, any array operation can be achieved by applying it. Recall that `map` and `filter` are special cases of `reduce`.

Let's combine what we've learned to solve a practical problem.

Many content management sites (CMS) have the titles of a post added to part of the URL for simple bookmarking purposes. For example, if you write a Medium post titled "Stop Using Reduce", it's likely the URL would have some form of the title string in it (".../stop-using-reduce"). You may have already noticed this on the freeCodeCamp site.

# --instructions--

Fill in the `urlSlug` function so it converts a string `title` and returns the hyphenated version for the URL. You can use any of the methods covered in this section, and don't use `replace`. Here are the requirements:

The input is a string with spaces and title-cased words

The output is a string with the spaces between words replaced by a hyphen (`-`)

The output should be all lower-cased letters

The output should not have any spaces

# --hints--

Your code should not use the `replace` method for this challenge.

```js
assert(!code.match(/\.?[\s\S]*?replace/g));
```

`urlSlug("Winter Is Coming")` should return `"winter-is-coming"`.

```js
assert(urlSlug('Winter Is Coming') === 'winter-is-coming');
```

`urlSlug(" Winter Is  Coming")` should return `"winter-is-coming"`.

```js
assert(urlSlug(' Winter Is  Coming') === 'winter-is-coming');
```

`urlSlug("A Mind Needs Books Like A Sword Needs A Whetstone")` should return `"a-mind-needs-books-like-a-sword-needs-a-whetstone"`.

```js
assert(
  urlSlug('A Mind Needs Books Like A Sword Needs A Whetstone') ===
    'a-mind-needs-books-like-a-sword-needs-a-whetstone'
);
```

`urlSlug("Hold The Door")` should return `"hold-the-door"`.

```js
assert(urlSlug('Hold The Door') === 'hold-the-door');
```

# --seed--

## --seed-contents--

```js
// Only change code below this line
function urlSlug(title) {


}
// Only change code above this line
```

# --solutions--

```js
// Only change code below this line
function urlSlug(title) {
  return title.trim().split(/\s+/).join("-").toLowerCase();
}
```