[Solved]-Outputting Value of Promise during multiple parses-d3.js

Assuming :

• you have a starting promise named csvPromise, which delivers array
• the methods to be applied are methodA, methodB, methodC etc, each of which accepts Array
• each method either returns a mutation of the input array or delivers the mutation via a Promise
• changes to the array are cumulative, method-on-method
• you have a synchronous function output() which will accept the original array and each mutation

then a pattern like this will do the job :

csvPromise
.then(function(arr) {
    output(arr); // observe initial array as delivered by csvPromise
    return methodA(arr);
})
.then(function(arr) {
    output(arr); // observe array after application of methodA
    return methodB(arr);
})
.then(function(arr) {
    output(arr); // observe array after application of methodB 
    return methodC(arr);
})
etc..
etc..
etc..
.then(function(arr) {
    output(arr); // observe array after application of final method
}).catch(function(error) {
    console.log(error); // any error thrown from anywhere in the chain will arrive here 
});

The pattern can be proceduralised by building the chain dynamically as follows :

var methods = [methodA, methodB, methodC, ...]; // list of methods (uncalled at this point)
return methods.reduce(function(promise, method) {
    return promise.then(function(arr) {
        output(arr); // observe result of previous stage
        return method(arr);
    });
}, csvPromise)
.then(function(arr) {
    output(arr); // observe array after application of final method
}).catch(function(error) {
    console.log(error); // any error thrown from anywhere in the chain will arrive here 
});

The most likely violation of the assumptions would be that output() was itself asynchronous, in which case :

var methods = [methodA, methodB, methodC, ...]; // list of methods
return methods.reduce(function(promise, method) {
    return promise.then(function(arr) {
        return output(arr).then(function() {
            return method(arr);
        });
    });
}, csvPromise)
.then(function(arr) {
    output(arr); // observe array after application of final method
}).catch(function(error) {
    console.log(error); // any error thrown from anywhere in the chain will arrive here 
});