Help with custom loadstring()?

So I've heard some people talk about actually CREATING a custom loadstring function to load code locally (typically in script builder). Is this even possible? How would you be able to make your own loadstring function?

-- I know this could be totally wrong, but this is the only thing i could come close to
-- even though it's probably way off.

local http = game:GetService("HttpService")
local source = http:GetAsync("URL")

local function parse_string(str)
    local c = ''
    for i in str:gmatch(".")do
        c = c..'\\'..i:byte()
    end
    return c
end

local function load(str)
    local l = ''
    for i in str:gmatch('[^\\]+')do
        if tonumber(i) and string.char(tonumber(i)) then
            l = l..string.char(tonumber(i))
        end
    end
    return l
end

loadstring(load(parse_string(source)))()

Don't laugh, but that's about as close to anything that i'm going to get regarding making a custom loadstring function. If somebody could help, or offer just the slightest of advice, i would very much appreciate it.

And as always, thank you for your time.