[BuyWidget] Handle very large numbers in FundWallet component

Author: joaquim-verges

.changeset/legal-fans-enjoy.md

@@ -0,0 +1,5 @@
+---
+"thirdweb": patch
+---
+
+Handle very large numbers in BuyWidget

packages/thirdweb/src/react/web/ui/Bridge/FundWallet.tsx

@@ -112,9 +112,7 @@ export function FundWallet({
     // Convert USD amount to token amount using token price
     const tokenAmount = usdAmount / uiOptions.destinationToken.priceUsd;
     // Format to reasonable decimal places (up to 6 decimals, remove trailing zeros)
-    const formattedAmount = Number.parseFloat(
-      tokenAmount.toFixed(6),
-    ).toString();
+    const formattedAmount = toPlainString(Number.parseFloat(tokenAmount.toFixed(6)));
     setAmount(formattedAmount);
   };
 
@@ -341,3 +339,36 @@ export function FundWallet({
     </WithHeader>
   );
 }
+
+function toPlainString(num: number) {
+  const str = num.toString();
+  
+  // If no exponential notation, return as-is
+  if (str.indexOf('e') === -1) {
+    return str;
+  }
+  
+  // Parse exponential notation
+  const parts = str.split('e');
+  const coefficient = parts[0];
+  const exponent = parseInt(parts[1] ?? '0');
+  
+  // Handle negative exponents (small numbers)
+  if (exponent < 0) {
+    const zeros = '0'.repeat(Math.abs(exponent) - 1);
+    const digits = coefficient?.replace('.', '') || '';
+    return '0.' + zeros + digits;
+  }
+  
+  // Handle positive exponents (large numbers)
+  const [integer, decimal = ''] = coefficient?.split('.') || [];
+  const zerosNeeded = exponent - decimal.length;
+  
+  if (zerosNeeded >= 0) {
+    return integer + decimal + '0'.repeat(zerosNeeded);
+  } else {
+    const insertAt = (integer?.length ?? 0) + zerosNeeded;
+    const result = integer + decimal;
+    return result.slice(0, insertAt) + '.' + result.slice(insertAt);
+  }
+}