fix: Implement toExponential polyfill for broader compatibility

Co-authored-by: aider (gemini/gemini-2.5-pro) <aider@aider.chat>

calculator/calculator.app.js

@@ -206,6 +206,29 @@ function subtract(x, y) {
   return sum(x, -y);
 }
 
+function toExponential(num, precision) {
+  if (num === 0) {
+    let z = "0";
+    if (precision > 0) z += "." + "0".repeat(precision);
+    return z + "e+0";
+  }
+  var sign = "";
+  if (num < 0) {
+    sign = "-";
+    num = -num;
+  }
+  var exp = Math.floor(Math.log10(num));
+  var mantissa = num / Math.pow(10, exp);
+
+  var mantissaFixed = mantissa.toFixed(precision);
+  if (parseFloat(mantissaFixed) >= 10) {
+      mantissaFixed = (mantissa/10).toFixed(precision);
+      exp++;
+  }
+
+  return sign + mantissaFixed + "e" + (exp >= 0 ? "+" : "") + exp;
+}
+
 function fixFloat(n) {
   if (Math.abs(n) < 1e-10) return 0;
   return n;
@@ -265,7 +288,7 @@ function displayOutput(num) {
     if (typeof num === 'number' && (numStr.length > RESULT_MAX_LEN || (num !== 0 && Math.abs(num) < 1e-4))) {
         let precision = RESULT_MAX_LEN - 8;
         if (precision < 0) precision = 0;
-        num = num.toExponential(precision).replace("e", "E");
+        num = toExponential(num, precision).replace("e", "E");
     } else {
         num = numStr;
     }