fix(send): use string type for sendTokenAmount to preserve precision - #5618
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Fixes REOWN-3617: Send/Swap max amount of token throws transaction error Root cause: sendTokenAmount was typed as number, causing JavaScript floating-point precision loss (~15-16 significant digits). For tokens with 18 decimals, amounts like 1.234567890123456789 became 1.2345678901234568, causing gas estimation to fail when the slightly incorrect amount exceeded the actual balance. Changes: - Changed sendTokenAmount type from number to string in SendController - Updated onMaxClick() to pass string directly (no Number() conversion) - Updated onInputChange() to convert input to string - Added NumberUtil.bigNumber() for balance comparisons - Aligned with SwapController.sourceTokenAmount pattern Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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svenvoskamp
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Apr 13, 2026
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Summary
Fixes Send/Swap max amount of token throwing transaction errors due to JavaScript floating-point precision loss (REOWN-3617).
Technical Report
Problem
When sending the max amount of a token with 18 decimals, the transaction fails because the amount exceeds the actual on-chain balance. The sent amount differs from the intended amount due to JS number precision limits.
Root Cause Analysis
sendTokenAmount was typed as number throughout the send flow (SendController, UI components, event tracking). JavaScript numbers (IEEE 754 double-precision) can only represent ~15-16 significant digits accurately. Tokens with 18 decimals can require up to 18+ significant digits. For example, a balance of 1.123456789012345678 ETH would be truncated/rounded by JS number arithmetic, and the resulting amount could exceed the actual balance by a tiny margin — causing the transaction to revert.
The critical point was w3m-input-token's onMaxClick handler: maxValue.toFixed(20) produced the correct string, but wrapping it in Number(...) immediately lost precision before it reached SendController.
Approach & Reasoning
Changed sendTokenAmount from number to string across the entire flow:
Number() conversion only at boundaries where it's safe:
Critical EVM path preserved full precision:
Why string and not BigInt: The value needs to flow through UI input fields, Lit property bindings, and valtio state — all of which handle strings naturally. BigInt would require constant conversion at every UI boundary.
Files Changed
Verification
Test plan
🤖 Generated with Claude Code