Why is firebug telling me my JavaScript array is undefined?

Question

Just started working on a basic grid analysis algorithm in JavaScript but I have come up against an error that is perplexing me.

var max = 9;
var testArray = new Array(
  ['7', '3', '9', '6', '4', '1', '5', '2', '8'],
  ['1', '8', '2', '7', '5', '3', '4', '6', '9'],
  ['9', '5', '7', '3', '8', '2', '1', '4', '6'],
  ['3', '1', '4', '9', '6', '7', '2', '8', '5'],
  ['6', '2', '8', '5', '1', '4', '9', '3', '7'],
  ['5', '4', '6', '2', '9', '8', '3', '7', '1'],
  ['8', '7', '1', '4', '3', '5', '6', '9', '2'],
  ['2', '9', '3', '1', '7', '6', '8', '5', '4']
);

function checkYoSelf(myGrid) {
  var i; var j;
  var horizLine = new String;
  for( i = 0; i <= (max - 1); i++ ) {
    for( j = 0; j <= (max - 1); j++) {
      document.write(i+"<br />");
      horizLine += myGrid[i][j];
    }
    var test = RegExp(i, "ig");
    var result = new Array(horizLine.match(test));
    if( result.length > 1 ) {
      alert("fail");
    }    
  }
}

html file has <a href='#' onclick="checkYoSelf(testArray);">check</a>

According to firebug myGrid[i] is undefined but I'm not sure why this should be.

What am I doing wrong?

I would like to propose to you i < max as opposed to i <= (max - 1). — chaos
– chaos, Commented Mar 25, 2009 at 22:29
Also, just use var horizLine = "". No need for new String. Same with arrays. arr = [ [1,2,3], [4,5,6], [7,8,9] ]; — Chetan S
– Chetan S, Commented Mar 25, 2009 at 22:37
To concatenate array elements into a string, just use Array.join(''). — Chetan S
– Chetan S, Commented Mar 25, 2009 at 22:42

Seb · Accepted Answer · 2009-03-25 22:37:03Z

2

Well, this is working for me... I've just replaced your "max" variable to something more dynamic:

<script type="text/javascript">
    var testArray = new Array(
        ['7', '3', '9', '6', '4', '1', '5', '2', '8'],
        ['1', '8', '2', '7', '5', '3', '4', '6', '9'],
        ['9', '5', '7', '3', '8', '2', '1', '4', '6'],
        ['3', '1', '4', '9', '6', '7', '2', '8', '5'],
        ['6', '2', '8', '5', '1', '4', '9', '3', '7'],
        ['5', '4', '6', '2', '9', '8', '3', '7', '1'],
        ['8', '7', '1', '4', '3', '5', '6', '9', '2'],
        ['2', '9', '3', '1', '7', '6', '8', '5', '4']
    );

    function checkYoSelf(myGrid) {
        var i;
        var j;
        var horizLine = new String;

        var maxRows = myGrid.length;
        for( i = 0; i < maxRows; i++ ) {
            var maxColumns = myGrid[i].length;
            for( j = 0; j < maxColumns; j++) {
                document.write(i+"<br />");
                horizLine += myGrid[i][j];
            }

            var test = RegExp(i, "ig");
            var result = new Array(horizLine.match(test));
            if( result.length > 1 ) {
                alert("fail");
            }
        }
    }
</script>

<a href='#' onclick="checkYoSelf(testArray);">check</a>

Not sure what you're trying to do with this, but at least it doesn't give any error.

answered Mar 25, 2009 at 22:37

Seb

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1 Comment

Nick Over a year ago

interesting, your version doesn't throw any errors however when I separate the javascript into a separate js file and source in the html head the same error that I mentioned earlier occurs. Clearly I need to work a lot harder at my javascript!

nickf · Accepted Answer · 2009-03-25 22:29:55Z

1

where is max coming from?

max is defined globally (in this case max = 9)

you only have 8 rows.

answered Mar 25, 2009 at 22:29

nickf

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2 Comments

Nick Over a year ago

max is defined globally (in this case max = 9)

Chetan S Over a year ago

@Nick: There are only 8 outer arrays.

chaos · Accepted Answer · 2009-03-25 22:31:56Z

0

From your comment to nickf's answer: it's because max is 9, but you only have 8 rows in the array.

answered Mar 25, 2009 at 22:31

chaos

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Comments

strager · Accepted Answer · 2009-03-25 22:36:57Z

0

testArray contains 8 elements. You're accessing testArray[8], which is invalid because the index must be 0..7 (0..8-1). Add another row to your array, or rewrite the first for as:

for( i = 0; i <= (max - 2); i++ ) {

answered Mar 25, 2009 at 22:36

strager

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2 Comments

nickf Over a year ago

max - 2? why not just set max to be the actual max?

strager Over a year ago

@nickf, I don't know. I'm working off the code I'm given. If you set the actual max (the variable), you'll be changing other parts of the code as well.

Russ Cam · Accepted Answer · 2009-03-25 22:39:34Z

0

Firebug says

max is not defined

You're trying to access testArray[8] inside checkYoSelf(testArray) when the last index is testArray[7].

edited Mar 25, 2009 at 22:39

answered Mar 25, 2009 at 22:32

Russ Cam

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Comments

Andy Mikula · Accepted Answer · 2009-03-25 23:24:44Z

0

If you rewrite

for( i = 0; i <= (max - 1); i++ ) {
   for( j = 0; j <= (max - 1); j++) {

as

for( i = 0; i < (max - 1); i++ ) {
   for( j = 0; j < max; j++) {

it should work. The first dimension of your grid is only 8.

answered Mar 25, 2009 at 23:24

Andy Mikula

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Comments

Nick · Accepted Answer · 2009-03-26 00:21:27Z

thanks to everyone for their help, the firebug error is no longer occuring now that the code is:

var testArray = new Array(
  ['7', '3', '9', '6', '4', '1', '5', '2', '8'],
  ['1', '8', '2', '7', '5', '3', '4', '6', '9'],
  ['9', '5', '7', '3', '8', '2', '1', '4', '6'],
  ['3', '1', '4', '9', '6', '7', '2', '8', '5'],
  ['5', '4', '6', '2', '9', '8', '3', '7', '1'],
  ['6', '2', '8', '5', '1', '4', '9', '3', '7'],
  ['8', '7', '1', '4', '3', '5', '6', '9', '2'],
  ['2', '9', '3', '1', '7', '6', '8', '5', '4'],
  ['2', '9', '3', '1', '7', '6', '8', '5', '4']
);

function checkYoSelf(myGrid) {
  var i;
  var j;
  var horizLine = new String;
  var max = myGrid.length;

  for( i = 0; i < max; i++ ) {
    for( j = 0; j < max; j++) {
      horizLine += myGrid[i][j];
    }
    var test = RegExp(i, "ig");
    var result = new Array(horizLine.match(test));
    if( result.length > 1 ) {
      alert("fail");
    }    
  }
}

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