使用不同的参数多次调用同一函数。 完成后：在其他函数中使用每个返回值

Question

Does anyone have an idea how to make a plausible promise chain for this asynchronous JavaScript code:

Updated:

var arr1 = firstFunc(input1, function(err, res){
    if(err) return err;
    return res;
});

var arr2 = firstFunc(input2, function(err, res){
    if(err) return err;
    return res;
});

// When above functions done call this func:

var arr3 = middleFunc(arr1, arr2, function(err, res){
    if(err) return err;
    return res;
});

// When above functions done call this func:

var arr4 = lastFuntion(arr3);

Answer 1

The functions as they stand are not currently promises. They do, however, follow the async pattern in node.

You can either use something like promisify-node or do it yourself:

// define the first 2 promises by calling firstFunc with inputs
var promise1 = new Promise(function resolver(resolve, reject) {
    firstFunc(input1, function(err, res){
        if(err) reject(err);
        resolve(res);
    });

var promise2 = new Promise(function resolver(resolve, reject) {
    firstFunc(input2, function(err, res){
        if(err) reject(err);
        resolve(res);
    });

// When promise1 & 2 resolve, execute the then handler
Promise.all([promise1, promise2]).then(function (arr) {
    // Grab the resolved values
    var arr1 = arr[0];
    var arr2 = arr[1];

    // return a new promise that is resolved when middleFunc completes
    return new Promise(function resolver(resolve, reject) {
        middleFunc(arr1, arr2, function(err, res){
            if(err) reject(err);
            resolve(res);
        });
    });
}).then(function (arr3) { // Execute this when middleFunc completes
     return lastFuntion(arr3); // This function looks synchronous
}).catch(function (err) {
    // Handle any errors along the way
});

Edit : If you want to create promise1 and promise2 more generically, write a helper function:

// Helper function to construct a promise by calling firstFunc with input
var firstFuncHelper = function (input) {
    return new Promise(function resolver(resolve, reject) {
        firstFunc(input, function(err, res){
            if(err) reject(err);
            resolve(res);
        });
};

var promise1 = firstFuncHelper(input1);
var promise2 = firstFuncHelper(input2);

// Rest of code above remains