Just another update

Task/LZW-compression/JavaScript/lzw-compression.js

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+//LZW Compression/Decompression for Strings
+var LZW = {
+    compress: function (uncompressed) {
+        "use strict";
+        // Build the dictionary.
+        var i,
+            dictionary = {},
+            c,
+            wc,
+            w = "",
+            result = [],
+            dictSize = 256;
+        for (i = 0; i < 256; i += 1) {
+            dictionary[String.fromCharCode(i)] = i;
+        }
+
+        for (i = 0; i < uncompressed.length; i += 1) {
+            c = uncompressed.charAt(i);
+            wc = w + c;
+            //Do not use dictionary[wc] because javascript arrays
+            //will return values for array['pop'], array['push'] etc
+           // if (dictionary[wc]) {
+            if (dictionary.hasOwnProperty(wc)) {
+                w = wc;
+            } else {
+                result.push(dictionary[w]);
+                // Add wc to the dictionary.
+                dictionary[wc] = dictSize++;
+                w = String(c);
+            }
+        }
+
+        // Output the code for w.
+        if (w !== "") {
+            result.push(dictionary[w]);
+        }
+        return result;
+    },
+
+
+    decompress: function (compressed) {
+        "use strict";
+        // Build the dictionary.
+        var i,
+            dictionary = [],
+            w,
+            result,
+            k,
+            entry = "",
+            dictSize = 256;
+        for (i = 0; i < 256; i += 1) {
+            dictionary[i] = String.fromCharCode(i);
+        }
+
+        w = String.fromCharCode(compressed[0]);
+        result = w;
+        for (i = 1; i < compressed.length; i += 1) {
+            k = compressed[i];
+            if (dictionary[k]) {
+                entry = dictionary[k];
+            } else {
+                if (k === dictSize) {
+                    entry = w + w.charAt(0);
+                } else {
+                    return null;
+                }
+            }
+
+            result += entry;
+
+            // Add w+entry[0] to the dictionary.
+            dictionary[dictSize++] = w + entry.charAt(0);
+
+            w = entry;
+        }
+        return result;
+    }
+}, // For Test Purposes
+    comp = LZW.compress("TOBEORNOTTOBEORTOBEORNOT"),
+    decomp = LZW.decompress(comp);
+document.write(comp + '<br>' + decomp);