Higher levels of granularity leading to undefined values in array return

Question

Higher levels of granularity leading to undefined values in array return

Currently, I am utilizing AJAX to parse a CSV file into an Object of Arrays. However, I am encountering an issue where the data seems to be successfully read and stored in the Object but when I try to access it at deeper levels, I receive undefined messages. It appears that everything is present in the Object upon initial inspection. My suspicion is that this issue may be related to timing, especially since I am dealing with significant amounts of data.

JS

$(document).ready(function () {
    var data = fetchCSVData();
    displayTable(data);
});

function fetchCSVData() {
    var data = {"columns":[], "rows":[]};

    $.ajax({
        url : 'assets/php/readCSV.php',
        type : 'POST',
        success : function (csv) {
            var colCount = csv[0].length,
                rowCount = csv.length;

            for (var c = 0; c < colCount; c++) {
                data['columns'][c] = csv[0][c];
            }

            csv.splice(0,1);

            for (var r = 0; r < rowCount; r++) {
                data['rows'][r] = csv[r];
            }
        },
        error : function () {
            alert("Error: Unable to read the CSV file. Please try again.");
        }
    });

    return data;
}

function displayTable(data) {
    console.log(data); // Successfully displays all data.
    console.log(data['columns']); // Displays columns data as expected
    console.log(data['columns'][0]); // Returns as undefined
}

Snippet from first console log

Object { columns=[0],  rows=[0]}
columns     ["EXPERIMNT CODE", "EXPERIMNT_NAME", "VarCode", 12 more...]
rows    [["H1225", "COP - Show star rating a...ting in the price panel", "H1225:001.000", 12 more...], ["H1225", "COP - Show star rating a...ting in the price panel", "H1225:001.001", 12 more...], ["H1225", "COP - Show star rating a...ting in the price panel", "H1225:001.002", 12 more...], 4873 more...]

Snippet from second console log

[]          
0   "EXPERIMNT CODE"
1   "EXPERIMNT_NAME"
2   "VarCode"
3   "VarName"
4   "Version Number"
5   "Reporting Range Start Date"
6   "Reporting Range End Date"
7   "Status"
8   "Transaction Date"
9   "EXPERIMNT TEST ID"
10  "Test Manager"
11  "Product Manager"
12  "Pod"
13  "Record_Update_Datetm"
14  "Insert_datetm"

The third log returns undefined despite the presence of data indicated in the second snippet.

Any insights on what might be causing this discrepancy?

javascript arrays ajax csv object

Answer 1

Answer №1

When it comes to Ajax, the "A" actually stands for "asynchronous". This means that the execution will not wait for a response after making an ajax request using $.ajax() in your readCSV() function. As a result, your readCSV() function will return before the response is received, likely returning {"columns":[], "rows":[]}. Even though the response gets processed later by the success callback, by then the populateTable() function has already been called.

A possible explanation for why the console logs display certain data could be that some browsers keep a live connection to the logged object. Initially, you might see Object { columns=[0], rows=[0]} because the arrays were empty when console.log(data) was executed (hence the zeros), and at that moment data['columns'][0] was probably undefined. However, when you expand the object in the console to view the array contents, the ajax response would have been received and the arrays filled with data.

To resolve this issue, a simple solution would be to call populateTable() from within the success handler, ensuring that the data is available at that point.

Answer 2

When it comes to Ajax, the "A" actually stands for "asynchronous". This means that the execution will not wait for a response after making an ajax request using $.ajax() in your readCSV() function. As a result, your readCSV() function will return before the response is received, likely returning {"columns":[], "rows":[]}. Even though the response gets processed later by the success callback, by then the populateTable() function has already been called.

A possible explanation for why the console logs display certain data could be that some browsers keep a live connection to the logged object. Initially, you might see Object { columns=[0], rows=[0]} because the arrays were empty when console.log(data) was executed (hence the zeros), and at that moment data['columns'][0] was probably undefined. However, when you expand the object in the console to view the array contents, the ajax response would have been received and the arrays filled with data.

To resolve this issue, a simple solution would be to call populateTable() from within the success handler, ensuring that the data is available at that point.

Higher levels of granularity leading to undefined values in array return

Answer №1

Similar questions

Is it possible to dynamically set a style attribute in a Model based on the field's value?

Using Grails with AJAX: remoteLink results in a page redirect instead of updating the specified div

Executing Javascript without invoking the default behavior

Incorporate an image into your webpage with the Fetch API by specifying the image link - JavaScript

Attempting to upload blob using FormData, but the file content is missing

Are certain browsers unable to play dynamically generated HTML5 audio files?

Add a font awesome icon dynamically using JavaScript

ajax request information received in the callback

Enjoy watching a video by simply hovering over the highlighted words

Issues with Django redirection functionality not functioning as expected

Using Jquery to load a URL using AJAX

Clicking on the Google Maps direction service can add additional markers to the map

Bespoke String Implementation

Working with multidimensional arrays in blade templates

Monitor modifications to an array and then send the updated array back to the original page

Experimenting with Selenium and JavaScript to run automated tests using Fancybox as a demonstration

Generate a collection of random numbers within a specific range, allowing for potential duplicates

Transferring and displaying messages between PHP scripts

After switching from jQuery to pure JavaScript, the code is now up and

Dynamically restricting the fields returned in MongoDB