diff --git a/public/js/main.js b/public/js/main.js
new file mode 100644
index 0000000..ee1222c
--- /dev/null
+++ b/public/js/main.js
@@ -0,0 +1,91 @@
+window.addEventListener("load", () => main());
+
+const input_name = "firstname";
+
+const main = () => {
+    // Reset content of the input
+    document.getElementById(input_name).value = "";
+
+    // Call callback when editing the input
+    document.getElementById(input_name).addEventListener("input", update_const);
+};
+
+// Callback: called when firstname is changed
+const update_const = () => {
+    const firstname = document.getElementById(input_name).value;
+    const firstname_const = get_const(firstname.split(''));
+
+    console.log(`output: ${firstname_const}`);
+};
+
+const get_const = (letters = Array) => {
+    console.log(`input: ${letters}`);
+
+    // Store constants of each letters of the firstname
+    let const_data = [];
+
+    // Store some constants info
+    //let const_infos = {};
+
+    // Assign each letter to a const, fallback to 1 if no one has been found
+    switch (letters) {
+        /* case 'a':
+            const_data.push(); */
+        /* case 'b':
+            const_data.push(); */
+        /* case 'c':
+            const_data.push(); */
+        /* case 'd':
+            const_data.push(); */
+        /* case 'e':
+            const_data.push(); */
+        /* case 'f':
+            const_data.push(); */
+        /* case 'g':
+            const_data.push(); */
+        /* case 'h':
+            const_data.push(); */
+        /* case 'i':
+            const_data.push(); */
+        /* case 'j':
+            const_data.push(); */
+        /* case 'k':
+            const_data.push(); */
+        /* case 'l':
+            const_data.push(); */
+        /* case 'm':
+            const_data.push(); */
+        /* case 'n':
+            const_data.push(); */
+        /* case 'o':
+            const_data.push(); */
+        /* case 'p':
+            const_data.push(); */
+        /* case 'q':
+            const_data.push(); */
+        /* case 'r':
+            const_data.push(); */
+        /* case 's':
+            const_data.push(); */
+        /* case 't':
+            const_data.push(); */
+        /* case 'u':
+            const_data.push(); */
+        /* case 'v':
+            const_data.push(); */
+        /* case 'w':
+            const_data.push(); */
+        /* case 'x':
+            const_data.push(); */
+        /* case 'y':
+            const_data.push(); */
+        /* case 'z':
+            const_data.push(); */
+
+        default:
+            const_data.push(1);
+    }
+
+    // Multiply all the constants together
+    return const_data.reduce((a, b) => a * b);
+};