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Cannot use "map" function within async module

Cannot use "map" function within async module

Problem

I am using node.js "async" module and need to use the "map" method.
Basically I have an array that contains other arrays. The inner arrays contains 2 elements, a type and an image filename.

var arr0 = [];
var arr1 = ["type1", "image1.jpg"];
jsonArr.push(obj1);
var arr2 = ["type2", "image2.jpg"];
jsonArr.push(obj2);

For each inner array, I want to get the base64 encoding of the image identified by the filename and add this encoding string as the third element of the array.

I'm doing something like this:

var fs = require("fs");
var async = require("async");

function getImageEncoding(arr, callback){
    console.log("getEncoding:" + arr + "\n");

    // Get image filename
    image = arr[1];

    // Read file and get base64 encoding
    fs.readFile(image, function(err, original_data){
    var base64Image = original_data.toString('base64');
    console.log("test:" + base64Image + "\n");

        // Modify current arr by appendingthe base64 encoding of the image
        callback(null, arr.push(base64Image));
    });
}

async.map(arr0, getImageEncoding, function(err, results){
console.log("in async.map: " + results + "\n");
});

I know the arr.push(base64Image) stuff is the thing that is not correct, but I cannot figure out how to return the modified element.

In map(arr, iterator, callback) documentation, it is specified:

"The iterator is called with an item from the array and a callback for when it has finished processing."

The thing is I cannot figure out how to feed the callback with the new arrays.

Problem courtesy of: Luc

Solution

This doesn't work because callback in getImageEncoding is called with the return value of arr.push (which is 1), not arr after arr.push, which is what you want.

function getImageEncoding(arr, callback){
    console.log("getEncoding:" + arr + "\n");

    // Get image filename
    image = arr[1];

    // Read file and get base64 encoding
    fs.readFile(image, function(err, original_data){
    var base64Image = original_data.toString('base64');
    console.log("test:" + base64Image + "\n");

        // Modify current arr by appendingthe base64 encoding of the image
        arr.push(base64Image);
        callback(err, arr);
    });
}

async.map(arr0, getImageEncoding, function(err, results){
console.log("in async.map: " + results + "\n");
});
Solution courtesy of: Nicocube

Discussion

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This post first appeared on Node.js Recipes, please read the originial post: here

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Cannot use "map" function within async module

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