Wraps a substring of a string with the given prefix and suffix, ignoring case for finding while still respecting it in the resulting string.

wrap.js

/** Wraps a substring with the given prefix and suffix in a string.
*
*@param  {String}	hay	The string in which the replacement is to occur.
*@param	{String}	needle	The string to look for. Will be wrapped without case sensitivity, but will respect the case of the original string.
@param	{String}	prefix	The string to insert before `needle`.
@param	{String}	suffix	The string to insert after `needle`.
*/
function wrap(hay, needle, prefix, suffix) {
	var lowHay		= hay.toLowerCase(),
		lowNeedle	= needle.toLowerCase(),
		index		= lowHay.indexOf(lowNeedle);

	if (index <= -1)
		return hay;

	return	hay.slice(0, index)
			+ prefix
			+ hay.slice(index, index + needle.length)
			+ suffix
			+ hay.slice(index + needle.length);
}