SOURCE

var list = []
var count = 0
var index = 0

var si1 = setInterval(() => {
    if(count<3) {
        var data = [...new Array(65)].map((item, index) => count + '' + index)
        list = [...list, ...data]
        console.log('input: ', list)
        count += 1 
    } else {
        window.clearInterval(si1)
    }
}, 1000)

var si2 = setInterval(() => {
    if(list[index*8]) {
        console.log('output: ', index*8, (index + 1)*8, list.slice(index*8, (index + 1)*8))
        index += 1
    } else {
        window.clearInterval(si2)
    }    
}, 1000)