Support alternative b64 characters

Coincidentally fixes #2 and fixes #7.

index.html

@@ -55,7 +55,7 @@
             <a href="https://git.fwdekker.com/FWDekker/converter/src/branch/master/LICENSE">MIT License</a>.
             Source code available on <a href="https://git.fwdekker.com/FWDekker/converter/">git</a>.
 
-            <div style="float: right;">v1.4.4</div>
+            <div style="float: right;">v1.4.5</div>
         </section>
     </footer>
 </main>
@@ -66,11 +66,40 @@
 <script src="https://cdnjs.cloudflare.com/ajax/libs/big-integer/1.6.44/BigInteger.min.js"
         integrity="sha256-es+ex6Oj344uak+VnCPyaHY2nzQkqhr7ByWVQgdjATA=" crossorigin="anonymous"></script>
 <script>
-    const stringReplaceAt =
-        (str, index, replacement) => str.substr(0, index) + replacement + str.substr(index + replacement.length);
-
-    const stringReplaceAll =
-        (str, target, replacement) => str.split(target).join(replacement);
+    /**
+     * Replaces the character at the given index with the given replacement.
+     *
+     * @param str the string to replace in
+     * @param index the index in the given string to replace at
+     * @param replacement the replacement to insert into the string
+     * @returns {string} the input string with one character replaced
+     */
+    const stringReplaceAt = (str, index, replacement) =>
+        str.substr(0, index) + replacement + str.substr(index + replacement.length);
+
+    /**
+     * Replaces all instances of the target with the replacement.
+     *
+     * @param str the string to replace in
+     * @param target the character to replace
+     * @param replacement the replacement to insert into the string
+     * @returns {string} the input string with all instances of the target replaced
+     */
+    const stringReplaceAll = (str, target, replacement) =>
+        str.split(target).join(replacement);
+
+    /**
+     * Runs `stringReplaceAll` for each character in `targets` and `replacements`.
+     *
+     * @param str the string to replace in
+     * @param targets the characters to replace
+     * @param replacements the replacements to insert into the string; each character here corresponds to a character
+     * in the targets string
+     * @returns {string} the input string with all instances of the targets replaced
+     */
+    const stringReplaceAlls = (str, targets, replacements) =>
+        Array.from(targets).reduce((output, target, index) =>
+            stringReplaceAll(output, target, replacements[index]), str);
 
 
     class NumeralSystem {
@@ -117,7 +146,7 @@
                     return;
 
                 this.textarea.value = this.numeralSystem.filterBaseString(this.textarea.value);
-                updateAllInputs(this.numeralSystem.baseToDecimal(this.textarea.value));
+                updateAllInputs(this, this.numeralSystem.baseToDecimal(this.textarea.value));
             };
         }
 
@@ -133,6 +162,17 @@
     }
 
     class Base64NumeralSystem extends NumeralSystem {
+        // TODO Convert static methods to static properties once supported by Firefox
+        static defaultAlphabet() {
+            return "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
+        }
+
+
+        /**
+         * Constructs a new base 64 numeral system.
+         *
+         * @param alphabet the 64 characters to encode numbers with, and the padding character at the end
+         */
         constructor(alphabet) {
             super(64, alphabet, true);
         }
@@ -148,11 +188,14 @@
                 .map(pair => String.fromCharCode(parseInt(pair.join(""), 16)))
                 .join("");
 
-            return btoa(b64);
+            return stringReplaceAlls(btoa(b64), Base64NumeralSystem.defaultAlphabet(), this.alphabet);
         }
 
         baseToDecimal(baseString) {
-            const hex = Array.from(atob(baseString))
+            if (baseString.length % 4 === 1) throw new Error("Invalid input string length.");
+
+            const normalBaseString = stringReplaceAlls(baseString, this.alphabet, Base64NumeralSystem.defaultAlphabet());
+            const hex = Array.from(atob(normalBaseString))
                 .map(char => char.charCodeAt(0).toString(16).padStart(2, "0")).join("");
             return bigInt(hex, 16);
         }
@@ -160,17 +203,13 @@
 
     class Base64NumeralSystemInput extends NumeralSystemInput {
         // TODO Convert static methods to static properties once supported by Firefox
-        static defaultAlphabet() {
-            return "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
-        }
-
         static dropdownOptions() {
             return {"Standard": ['+', '/'], "Filename": ['-', '_'], "IMAP": ['+', ',']};
         }
 
 
         constructor(name) {
-            super(name, new Base64NumeralSystem(Base64NumeralSystemInput.defaultAlphabet()));
+            super(name, new Base64NumeralSystem(Base64NumeralSystem.defaultAlphabet()));
 
             this.dropdownLabel = document.createElement("label");
             this.dropdownLabel.setAttribute("for", `${this.name}Dropdown`);
@@ -236,9 +275,10 @@
         ),
     ];
 
-    const updateAllInputs = newValue => {
+    const updateAllInputs = (source, newValue) => {
         for (const input of inputs)
-            input.update(newValue);
+            if (input !== source)
+                input.update(newValue);
     };
 
 
@@ -248,7 +288,7 @@
         for (const input of inputs)
             input.addToParent(inputParent);
 
-        updateAllInputs(bigInt(42));
+        updateAllInputs(undefined, bigInt(42));
         inputs[0].textarea.focus();
     });
 </script>