Error: Javascript is unable to read the length property of an undefined object

Question

Error: Javascript is unable to read the length property of an undefined object

I am encountering an issue where I am unable to utilize the .length() method on a data array in javascript. My goal is to iterate through an array of date time strings to convert them into date objects using javascript. Included below is my code.

Sample data:

HTTP 200 OK
Allow: GET, HEAD, OPTIONS
Content-Type: application/json
Vary: Accept

{
  "sales_time_axis": [
    [
      "2019-12-29T10:42:25Z"
    ],
    [
      "2019-12-23T03:13:03Z"
    ],
    [
      "2019-12-23T02:50:51Z"
    ]
  ],

The ajax call:

$.ajax({
  type: "GET",
  url: endpoint,    
  success: function(data) {
    window.sales_time = data.sales_time_axis
  },
  error: function(error_data) {
    console.log('error')
    console.log(error_data)
  }
})

The for loop:

var sales_time;
var date_array = []

for(i = 0 ; i < sales_time.length ; i++){
  date_array.push(new Date(sales_time[i]))
}

console.log(data_array)

I have defined sales_time as a global variable, yet I am receiving the following error:

(index):179 Uncaught TypeError: Cannot read property 'length' of undefined
at (index):179

Your assistance would be greatly valued!

javascript arrays ajax date

Answer 1

Answer №1

It seems like you may be encountering an issue with asynchronous variable assignment. To address this, try combining the for-loop with the success callback and iterate over the same sales_time variable that is being received as a callback parameter.

$.ajax({
  type: "GET",
  url: endpoint,    
  success: function(data){
    var sales_time = data.sales_time_axis;
    var date_array = []
    for(i = 0 ; i < sales_time.length ; i++){
      date_array.push(new Date(sales_time[i]))
    }
    console.log(data_array)
  },
  error: function(error_data){
    console.log('error')
    console.log(error_data)
  }
})

Answer 2

It seems like you may be encountering an issue with asynchronous variable assignment. To address this, try combining the for-loop with the success callback and iterate over the same sales_time variable that is being received as a callback parameter.

$.ajax({
  type: "GET",
  url: endpoint,    
  success: function(data){
    var sales_time = data.sales_time_axis;
    var date_array = []
    for(i = 0 ; i < sales_time.length ; i++){
      date_array.push(new Date(sales_time[i]))
    }
    console.log(data_array)
  },
  error: function(error_data){
    console.log('error')
    console.log(error_data)
  }
})

Answer 3

Answer №2

Make sure to wait for the asynchronous ajax call to finish before proceeding

For more information, check out this link: How to properly await an ajax request?

Answer 4

Make sure to wait for the asynchronous ajax call to finish before proceeding

For more information, check out this link: How to properly await an ajax request?

Answer 5

Answer №3

It has been noted by others that ajax operates asynchronously, meaning anything outside of the ajax call will run synchronously without waiting for the data to return. One approach to address this is by placing the iteration method as a callback inside the ajax success method with the data passed as an argument.

$.ajax({
    // SOME CONFIGS HERE
    success: function(result){
        iterate(result);
    }
});

function iterate(data){
    // Perform iteration here
}

If you prefer utilizing global variables, you can do it like this:

// Assuming all these are within the same JavaScript file

var data = []; // Define this as a global variable in your file 

$.ajax({
    // SOME CONFIGS HERE
    success: function(result){
        data = result.data;
        iterate(); // Retrieve data, then proceed with the iteration process
    }
});

function iterate(){
    // Perform iteration here
    data.forEach(() => { // Additional processing here });
}

This approach ensures that theiterate function is only called after the successful completion of the call. Attempting to call iterate outside the success method will result in an empty array.

Your coding mindset needs to shift if your workflow depends on a promise being fulfilled first. It's essential to execute the next step only after the promise has resolved, rather than executing it while the promise is still pending.

Answer 6

It has been noted by others that ajax operates asynchronously, meaning anything outside of the ajax call will run synchronously without waiting for the data to return. One approach to address this is by placing the iteration method as a callback inside the ajax success method with the data passed as an argument.

$.ajax({
    // SOME CONFIGS HERE
    success: function(result){
        iterate(result);
    }
});

function iterate(data){
    // Perform iteration here
}

If you prefer utilizing global variables, you can do it like this:

// Assuming all these are within the same JavaScript file

var data = []; // Define this as a global variable in your file 

$.ajax({
    // SOME CONFIGS HERE
    success: function(result){
        data = result.data;
        iterate(); // Retrieve data, then proceed with the iteration process
    }
});

function iterate(){
    // Perform iteration here
    data.forEach(() => { // Additional processing here });
}

This approach ensures that theiterate function is only called after the successful completion of the call. Attempting to call iterate outside the success method will result in an empty array.

Your coding mindset needs to shift if your workflow depends on a promise being fulfilled first. It's essential to execute the next step only after the promise has resolved, rather than executing it while the promise is still pending.

Error: Javascript is unable to read the length property of an undefined object

Answer №1

Answer №2

Answer №3

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