compress-decompress

compress.js

var log = console.log

var input = 'LLLAABBBBBEE'
log(input)

var c = compress(input)
log(c)

var d = decompress(c)
log(d)

function compress (str)
{
	return str
	.match(/(.)\1*/g)
	.map(chunk =>
	{
		var initial = chunk.charAt(0)
		var length  = chunk.length

		if (length > 2)
		{
			return `${ initial }${ length }`
		}
		else
		{
			return chunk
		}
	})
	.join('')
}

function decompress (str)
{
	return str
	.match(/\w\d+|\w\w/g)
	.map(chunk =>
	{
		var mm = chunk.match(/(\w)(\d+)/)

		if (mm)
		{
			var initial = mm[1]
			var length  = Number(mm[2])

			return initial.repeat(length)
		}
		else
		{
			return chunk
		}
	})
	.join('')
}