The length of the JavaScript array is not accurate

In my code, there is an array named 'plotData' which contains multiple 'rows' of data, each represented by a 4-element array. The array 'plotData' gets updated by a $.post() function further down in the script. The placeholders '...' indicate where some variables from the post request are utilized.

console.log("plotData (before update): ", plotData);
console.log("plotData length: ", plotData.length);

...
...
...

$.post(
    "/csvgen",
    {node_num: nodes.toString(), start_time: startTime.toString(), end_time: endTime.toString()},
    function(data){
        var nodeData = $.csv.toArrays(data);

        nodeData.forEach(function(element){
            plotData.push(element);
        });
    },
    "text"
);

I expected the method calls for logging the array and its length to execute in sequence. However, upon checking the console output, I noticed that while the console log of the array shows 28 entries, the plotData.length output indicates only 14. As new elements are added to the array, it consistently appears to be 14 more than what is displayed as plotData.length.

The 'plotData' array is accessed elsewhere in the code but remains unaltered.

Why might this discrepancy occur?

Edit to add log

Can't plot empty data set
TypeError: Cannot read property 'length' of undefined(…)
plotData (before update):  []
plotData length:  0
plotData (before update):  [Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4]]
plotData length:  14
plotData (before update):  [Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4], Array[4]
plotData length:  50

The initial error message occurs due to attempting to plot with an empty dataset.

Answer №1

Make sure to include logging statements at the end of your callback function to show the updated values after new rows are added. This will provide you with accurate information about the status of your code.

Answer №2

The issue is with the debugger in Chrome that I am currently using, not with the code itself. The code is running correctly as expected.

When using the "console.log()" function, individual values are logged successfully. However, when logging an array, no values are displayed. Instead, the debugger simply notes that the array was logged. When the user opens the array within the log, it dynamically generates the array based on its contents at that moment.

To correlate this information with the symptoms experienced, while the length of the array was being logged accurately, a reference to the array was logged instead. By the time the breakpoint was reached, the post request had returned and added data to the 'plotData' array. This caused the discrepancy between the displayed plotData.length and the actual length upon halting execution.

Credit for solving this issue goes to alexdmejias (refer to the comments). Thank you!

Answer №3

Ensure that you log the length within the callback function. Your current code attempts to log the length before the response is received, causing the array to be incomplete and the callback not triggered yet.

You may find this documentation helpful for further clarification.

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