Calling index of an array in loop causing error

Question

So I basically import a JSON file. I get back many arrays and each array has 4 elements in it. I want to parse the 3rd element from each array into it's own variable array.

$("#nextQ").click(function() {

  var Quotes = [];
  var totalQ //The total number of available quotes to choose from

  //Get quotes from JSON file
  $.ajax({
    url: '../facts.json',
    datatype: 'json',
    type: 'get',
    success: function(data) {
      console.log(data[0][2]); //This WORKS
      console.log(data.length); //Returns 64

      totalQ = data.length;

      for (i = 0; i <= totalQ; i++) {
        Quotes[i] = data[3][2]; //This WORKS
        Quotes[i] = data[i][2]; //This gives ERROR

      }
    }
  });

});

When I use data[i][2] I get this error: Uncaught TypeError: Cannot read property '2' of undefined. However this error doesn't occur if I use data[6][2] or any other number.

Thanks, any idea why that would give me an error on the 2nd index and not the 64th? — Badrush
– Badrush, Commented Mar 5, 2016 at 5:39
@Badrush - the first index in an array is zero, yet length really starts at one, as the length would be 1 if the array had one item, but that item would be at array[0]. When you loop, you loop to array.length - 1, but you're looping until i is the same as the length, so you're trying to look up array[length], which doesn't exists — adeneo
– adeneo, Commented Mar 5, 2016 at 5:42
@Badrush , data[data.length] will be undefined, you are trying to get the property of undefined. The property you are trying to access is 2 which is undefinded. — Pranav C Balan
– Pranav C Balan, Commented Mar 5, 2016 at 5:51

Pranav C Balan · Accepted Answer · 2016-03-05 05:49:52Z

3

You need to update the for loop condition from i <= totalQ; to i <totalQ; , since index starts from 0

for (i = 0; i < totalQ; i++) {
    Quotes[i] = data[i][2]; 
}

Or you can use $.each() as @adeneo suggested

$.each(data,function(i,v){
  Quotes[i] = v[2]; 
})

Or you can use native javascript map()

Quotes = data.map(function(v){
  return v[2]; 
})

edited Mar 5, 2016 at 5:49

answered Mar 5, 2016 at 5:39

Pranav C Balan

115k25 gold badges172 silver badges195 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Badrush Over a year ago

Thanks man, this worked. I would have caught this if the error hadn't told me the issue was with the 2nd index (random???)

Pranav C Balan Over a year ago

@Badrush , data[data.length] will be undefined, you are trying to get the property of undefined

Collectives™ on Stack Overflow

Calling index of an array in loop causing error

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related