jQuery script to populate a specified input with a suggested slug. For example, if I write 'My Title' in a title field, it can populate the slug field with a suggestion of 'my_title'.

readme.txt

Video demo at http://screencast.com/t/WcjpL2lc.

By default it uses a title field ending in [title] or [name] as the source field, and a field ending in [slug] as the destination. This matches the naming conventions for a framework like CakePHP, i.e. <?php echo $form->input('title'); ?> outputs an input with a name of data[Model][title]. 

You can override the default source and destination fields by setting document.slugField and document.titleField in JavaScript beforehand:

<script>
	document.titleField = "input[name$='[heading]']";
	document.slugField = "input[name$='[url_safe_heading]']";
</script>

You can specify multiple source fields, which the script will concatenate together into one slug:

<script>
	document.titleField = "input[name$='[first_name]'], input[name$='[last_name]']";
</script>

If the slug is manually overridden, no further suggestions are given.

slug.js

$(document).ready(function() {
	
	// Set some defaults.
	if(typeof document.titleField == 'undefined') {
		document.titleField = "input[name$='[title]'],input[name$='[name]']";
	}
	if(typeof document.slugField == 'undefined') {
		document.slugField = "input[name*='slug']";
	}

	var hasEdited = false;

	// If there's a slug already present, and it looks different to what would have been generated from the current title, deduced that the slug has already been manually edited.
	if($(document.slugField).attr('value') != '' && slugify(getTitle()) != $(document.slugField).attr('value')) {
		hasEdited = true;
		$(document.slugField).css('color', '#000');
	}

	// Colour the slug field grey to imply that magic is happening.
	$(document.slugField).css('color', '#666');
	
	// Generate the slug automatically as soon as the script loads, as the 'title' field may have been prepopulated with a value.
	populateSlugField($(document.titleField));

	// Generate a new slug each time the title has been edited. 
	$(document.titleField).keyup(function() {
		populateSlugField();
	});

	// Check for a manual override of the generated slug. Once the slug has been manually overridden, automatic slug generation should stop. 
	$(document.slugField).change(function() {
		console.log('slug field has been edited');
		hasEdited = true;
		$(this).css('color', '#000');
	});
	
/**
 * Populates the 'slug' field with a URL-safe version of the 'title' field.
 */
	function populateSlugField() {
		if(!hasEdited && $(document.titleField).length > 0) {
			slug = slugify(getTitle());
			$(document.slugField).val(slug);
		}
	}

/**
 * Converts text to a URL-safe form. For example, 'My Title' would become 'my_title'.
 *
 * @param  string  text The text to be slugified.
 * @return string		Slugified text
 */	
	function slugify(text) {
		text = text.toLowerCase();
		
		// Remove any characters that aren't URL-safe.
		slug = text
			// Replace spaces.
			.replace(/\s+/g, '_')
			// Replace special characters.
			.replace(/[àáâãäå]/g, 'a')
			.replace(/æ/g, 'ae')
			.replace(/ç/g, 'c')
			.replace(/[èéêë]/g, 'e')
			.replace(/[ìíîï]/g, 'i')
			.replace(/ñ/g, 'n')                        
			.replace(/[òóôõöø]/g, 'o')
			.replace(/œ/g, 'oe')
			.replace(/[ùúûü]/g, 'u')
			.replace(/[ýÿ]/g, 'y')
			// In what's left, remove anything that isn't URL-safe. 
			.replace(/[^a-z0-9_-]/g, '');
			
		return slug; 
	}

/**
 * Fetches source text to be slugified. This might come from just one field, or be concatenated from multiple fields.
 *
 * @return	string	Title text 
 */	
	function getTitle() {
		if($(document.titleField).size() > 1) {
			// As multiple title fields have been defined, concatenate them.
			title = '';
			i = 0;
			$(document.titleField).each(function() {
				if(i > 0 && title.length > 0 && this.value.length > 0) {
					title += '_';
				}
				title += this.value;
				i++;
			});
		} else {
			title = $(document.titleField).val();
		}
		
		return title;
	}
});

Thanks for this gist! Nice work!