Javascript Uncaught TypeError: Cannot read property ‘0’ of undefined

The error is here:

hasLetter("a",words[]);

You are passing the first item of words, instead of the array.

Instead, pass the array to the function:

hasLetter("a",words);

Problem solved!

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Here’s a breakdown of what the problem was:

I’m guessing in your browser (chrome throws a different error), words[] == words[0], so when you call hasLetter("a",words[]);, you are actually calling hasLetter("a",words[0]);. So, in essence, you are passing the first item of words to your function, not the array as a whole.

Of course, because words is just an empty array, words[0] is undefined. Therefore, your function call is actually:

hasLetter("a", undefined);

which means that, when you try to access d[ascii], you are actually trying to access undefined[0], hence the error.