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copied!<p>The <code>undefined</code> is a result of not initializing <code>c_text</code> before you try concatenate it with <code>_x</code>.</p> <p>The code only works on one letter because <code>alphabet.indexOf(x)</code> returns <code>-1</code> (not found). When using <code>o_text = "abc"</code>, <code>x</code> equals 0, 1, and 2. Thus, the index of 0, 1, or 2 in <code>alphabet</code> is nonexistent (indicated by the <code>-1</code> result). You need to relate those numbers back to <code>o_text</code> by changing <code>indexOf(x)</code> to <code>indexOf(o_text[x])</code>. Also, to prevent going outside the bounds of your array, you need a modulus operation to wrap values greater than 26 (I've used <code>alphabet.length</code> to allow this code to work with other alphabets) back around into a valid region. Thus, the correct code would be as follows (note: I've moved 'w' in your array into its proper location alphabetically, as I assumed its location in your example was an error and not intentional):</p> <pre><code>var currentkey = 5 //for example function convertKey(str) { var o_text = str; var o_letters = o_text.split(""); var alphabet = ['a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'] var c_text="", _x = ""; for (x in o_letters) { if (currentkey > 0) { _x = alphabet[(alphabet.indexOf(o_letters[x]) + currentkey) % alphabet.length] } else { _x = alphabet[(alphabet.indexOf(o_letters[x]) + (26 - currentkey)) % alphabet.length] } c_text = c_text + _x; } return c_text; } alert(convertKey('abcdefghijklmnopqrstuvwxyz')); </code></pre> <p>This alert's <code>fghijklmnopqrstuvwxyzabcde</code></p>

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