test-coroutine.lua

local co

local fetch = function(url)
    local promise = js.global:fetch(url)
    promise["then"](promise, function(_, res)
        local jsonPromise = res:json()
        jsonPromise["then"](jsonPromise, function(_, json)
            co(json)
        end)
    end)
    local res = coroutine.yield()
    return res
end

local fetchAll = function(...)
    local requests = {...}
    for i = 1, #requests do
        local promise = js.global:fetch(requests[i])
        promise["then"](promise, function(_, res)
            local jsonPromise = res:json()
            jsonPromise["then"](jsonPromise, function(_, json)
                co(i, json)
            end)
        end)
    end

    local results = {}
    for i = 1, #requests do
        local requestId, response = coroutine.yield()
        results[requestId] = response
    end

    return results
end

co = coroutine.wrap(function()
    local bird1 = fetch("http://apiv3.iucnredlist.org/api/v3/species/loxodonta%20africana?token=9bb4facb6d23f48efbf424bb05c0c1ef1cf6f468393bc745d42179ac4aca5fee")
    local bird2 = fetch("http://apiv3.iucnredlist.org/api/v3/species/Fratercula%20arctica/region/europe?token=9bb4facb6d23f48efbf424bb05c0c1ef1cf6f468393bc745d42179ac4aca5fee")

    print("Sequential: ", bird1.name, bird2.name)

    local birds = fetchAll(
        "http://apiv3.iucnredlist.org/api/v3/species/loxodonta%20africana?token=9bb4facb6d23f48efbf424bb05c0c1ef1cf6f468393bc745d42179ac4aca5fee",
        "http://apiv3.iucnredlist.org/api/v3/species/Fratercula%20arctica/region/europe?token=9bb4facb6d23f48efbf424bb05c0c1ef1cf6f468393bc745d42179ac4aca5fee"
    )

    print("Parallel: ")
    for i = 1, #birds do
        print(birds[i].name)
    end
end)

co()