Cannot read property length of undefined array error in JavaScript?

Question

I am using the code below to get a list of colours used by 3 divs. If this div has a color set, then it should be pushed into the array checkColors.

var checkColors = [];

$("div[style]").each(function(){
    getColor = $(this).css("color");
    if(getColor){
        checkColors.push(getColor);
    }
});

if(checkColors){
    checkColors = shuffleArray(checkColors);
    if(checkColors.length > 0){
        if(checkColors[0]){
            backgroundColor = checkColors[0];
        }
        if(checkColors[1]){
            primaryColor = checkColors[1];
        }
        if(checkColors[2]){
            secondaryColor = checkColors[2];
        }
    }  
}

However, if(checkColors.length > 0){ gives me a Uncaught TypeError: Cannot read property 'length' of undefined error which I don't understand since I have an If statement to check whether or not the array is undefined.

Here is the shuffleArray() function:

    function shuffleArray(array) {
        for (var i = array.length - 1; i > 0; i--) {
            var j = Math.floor(Math.random() * (i + 1));
            var temp = array[i];
            array[i] = array[j];
            array[j] = temp;
        }
    }

Clearly, calling shuffleArray is resulting in undefined, which is getting assigned to checkColors. It's probably missing a return xyz, but since you haven't shown it... — T.J. Crowder
– T.J. Crowder, Commented Mar 29, 2018 at 16:55
@scrappedcola: if (checkColors) is just fine, but as Jonas pointed out above, in the given code it'll always be true. (Also: typeof is an operator, not a function. No more need to put its operand in () than any other operator.) — T.J. Crowder
– T.J. Crowder, Commented Mar 29, 2018 at 16:56
Well, indeed there is no "return" in shuffleArray function, the shuffle array mutates the array and does return nothing. — Pac0
– Pac0, Commented Mar 29, 2018 at 16:57

Pac0 · Accepted Answer · 2018-03-29 16:58:31Z

4

I guess that

 shuffleArray(checkColors)

mutates the array instead of returning a new one. Therefore

 checkColors = shuffleArray(checkColors)

will set shuffleArray to undefined.

edited Mar 29, 2018 at 16:58

Pac0

23.4k9 gold badges76 silver badges85 bronze badges

answered Mar 29, 2018 at 16:55

Jonas Wilms

139k20 gold badges164 silver badges164 bronze badges

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

1 Comment

Jonas Wilms Over a year ago

Stop upvoting. I dont deserve reputation for this.

Rushikesh Bharad · Accepted Answer · 2018-03-31 05:36:20Z

0

You are already manipulating the array inside shuffleArray, do not assign it again to checkColors.

Below code change should work -

// checkColors = shuffleArray(checkColors);
// replace above line with
shuffleArray(checkColors);

Otherwise you need to return an array from shuffleArray if you are assigning it to checkColors.

function shuffleArray(array) {
   // your code
   // after for loop
   return array;
}

answered Mar 31, 2018 at 5:36

Rushikesh Bharad

1,0107 silver badges6 bronze badges

Collectives™ on Stack Overflow

Cannot read property length of undefined array error in JavaScript?

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related