palindrome.js

var input = 'FourscoreandsevenyearsagoourfaathersbroughtforthonthiscontainentanewnationconceivedinzLibertyanddedicatedtothepropositionthatallmenarecreatedequalNowweareengagedinagreahtcivilwartestingwhetherthatnaptionoranynartionsoconceivedandsodedicatedcanlongendureWeareqmetonagreatbattlefiemldoftzhatwarWehavecometodedicpateaportionofthatfieldasafinalrestingplaceforthosewhoheregavetheirlivesthatthatnationmightliveItisaltogetherfangandproperthatweshoulddothisButinalargersensewecannotdedicatewecannotconsecratewecannothallowthisgroundThebravelmenlivinganddeadwhostruggledherehaveconsecrateditfaraboveourpoorponwertoaddordetractTgheworldadswfilllittlenotlenorlongrememberwhatwesayherebutitcanneverforgetwhattheydidhereItisforusthelivingrathertobededicatedheretotheulnfinishedworkwhichtheywhofoughtherehavethusfarsonoblyadvancedItisratherforustobeherededicatedtothegreattdafskremainingbeforeusthatfromthesehonoreddeadwetakeincreaseddevotiontothatcauseforwhichtheygavethelastpfullmeasureofdevotionthatweherehighlyresolvethatthesedeadshallnothavediedinvainthatthisnationunsderGodshallhaveanewbirthoffreedomandthatgovernmentofthepeoplebythepeopleforthepeopleshallnotperishfromtheearth';

function sliceNDice(input){
	
	var  i
		,pairs = [];

	for(i = 0; i < input.length; i++){
		if(i + 1 < input.length){
			if(input[i] == input[i+1]) pairs.push( [i, i+1] );
		} 
	}

	recu(input, pairs, [0,0]);

}

function recu(input, pairs, longestRange){

	var  pair
		,start
		,end
		,toTest
		,newStart
		,newEnd
		,nextPairs = []

		,rangeLength = longestRange[1] - longestRange[0]
		,newRange = [];

	for(i = 0; i < pairs.length; i++){
		
		pair = pairs[i];
		start = pair[0];
		end = pair[1];
		toTest = input.substring(start, end - start);
		newStart = null;
		newEnd = null;
		
		if(start - 1 > -1) {
			toTest = input[start-1] + toTest;
		}

		if(toTest == toTest.split('').reverse().join('')){
			// found a palindrome by going back one
			newStart = start - 1;
		} else {
			newStart = start;
		}

		if(end + 1 < input.length) {
			toTest = toTest + input[end+1];
		}

		if(toTest == toTest.split('').reverse().join('')){
			// found a palindrome by going forward one
			newEnd = end + 1;
		} else {
			newEnd = end;
		}

		nextPairs.push( [newStart, newEnd] );
	}

	// find longest so far
	for(i = 0; i < nextPairs.length; i++){
		pair = nextPairs[i];
		start = pair[0];
		end = pair[1];

		if(end - start > rangeLength){
			newRange[0] = start;
			newRange[1] = end;
			rangeLength = end - start;
		} else {
			newRange = longestRange;
		}
	}

	console.log('longest range: ', longestRange);
	console.log('longest range as text: ', input.substring( longestRange[0], longestRange[1] - longestRange[0] ) );
	recu(input, nextPairs, newRange);
}

sliceNDice(input);