reduce (JavaScript Array Method)

const tnwNum = [70, 30, 20, 10, 7];

function tnwFun1(){
    document.getElementById("demo").innerHTML = tnwNum.join("
");
}

function tnwFun2(){
    var result = tnwNum.reduce(tnwFun3);
    document.getElementById("demo").innerHTML = result;
}

function tnwFun3(leftNum, sum){
    return leftNum - sum;
}