求解这段代码如何优化,在线等

function async_add(m, n, callback) {
setTimeout(callback.bind(null, m + n), 500);
}
async_add(1, 2, function(res) {
console.log(res); //3
async_add(res, 3, function(res) {
console.log(res); //6
async_add(res, 5, function(res) {
console.log(res); //11
async_add(res, 10, function(res) {
console.log(res); //21
async_add(res, 25, function(res) {
console.log(res); //46
async_add(res, 37, function(res) {
console.log(res); //83
async_add(res, 48, function(res) {
console.log(res); //131
})
})
});
});
});
});
});