TypeScript SDK: Types (Move ↔ TypeScript)#

Purpose#

Guide type mapping between Move and TypeScript when using @aptos-labs/ts-sdk: numeric types (especially u128/u256), address, TypeTag, and functionArguments / typeArguments.

ALWAYS#

1. Use bigint for u128 and u256 – in both view results and functionArguments; JavaScript number loses precision above 2^53.
2. Use string for address in payloads – e.g. "0x1" or accountAddress.toString(); SDK accepts AccountAddressInput (string or AccountAddress).
3. Use typeArguments for generic Move functions – e.g. coin type ["0x1::aptos_coin::AptosCoin"] for coin::balance or coin::transfer.
4. Cast view results explicitly when you know the Move return type – e.g. BigInt(result[0] as string) for u128.

NEVER#

1. Do not use number for u128/u256 – precision loss; use bigint.
2. Do not pass raw number for large u64 in entry/view – use bigint if value can exceed Number.MAX_SAFE_INTEGER.
3. Do not omit typeArguments when the Move function has type parameters (e.g. balance<CoinType>).

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Move → TypeScript (summary)#

Move typeTypeScript typeExampleu8, u16, u32number255, 65535u64number | bigintPrefer bigint for large valuesu128, u256bigintBigInt("340282366920938463463374607431768211455")i8..i64 (Move 2.3+)number | bigintUse bigint for i64 when largei128, i256bigintBigInt("-...")boolbooleantrueaddressstring"0x1"signer—Not passed from TS; signer is the transaction sendervectorUint8Array | string (hex)new Uint8Array([1,2,3]) or hexvectorT[][1, 2, 3]Stringstring"hello"Objectstring (object address)objectAddress.toString()OptionT | nullValue or null

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functionArguments#

Order and types must match the Move entry/view function parameters:

typescript

// Move: public fun transfer<CoinType>(to: address, amount: u64)
await aptos.transaction.build.simple({
  sender: account.accountAddress,
  data: {
    function: "0x1::coin::transfer",
    typeArguments: ["0x1::aptos_coin::AptosCoin"],
    functionArguments: [
      "0xrecipient...", // address as string
      1000n // u64 as bigint (or number if small)
    ]
  }
});

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typeArguments#

For generic Move functions, pass full type strings ( address::module::StructName):

typescript

// Move: balance<CoinType>(addr): u64
typeArguments: ["0x1::aptos_coin::AptosCoin"];

// Move: transfer<CoinType>(to, amount)
typeArguments: ["0x1::aptos_coin::AptosCoin"];

---

View return types#

typescript

const result = await aptos.view({
  payload: {
    function: "0x1::coin::balance",
    typeArguments: ["0x1::aptos_coin::AptosCoin"],
    functionArguments: [accountAddress]
  }
});
// result is an array; u128 often returned as string in JSON
const balance = BigInt(result[0] as string);

---

TypeTag (advanced)#

When building payloads programmatically or parsing type strings:

typescript

import { TypeTag } from "@aptos-labs/ts-sdk";

// Parser for type tag strings
import { parseTypeTag } from "@aptos-labs/ts-sdk";
const tag = parseTypeTag("0x1::aptos_coin::AptosCoin");

Use typeArguments as string array in simple cases; use TypeTag when the SDK API expects it.

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Object / resource address in arguments#

Pass object address as string (LONG or SHORT per AIP-40):

typescript

functionArguments: [
  nftObjectAddress.toString(), // or "0x..."
  price
];

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Common mistakes#

MistakeCorrect approachPassing number for u128 amountUse 1000000n or BigInt("...")Omitting typeArguments for coin::balanceAdd typeArguments: ["0x1::aptos_coin::AptosCoin"]Using result[0] as number for u128Use BigInt(result[0] as string)Wrong order of functionArgumentsMatch Move parameter order exactly

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References#

• SDK: src/transactions/typeTag/, src/transactions/instances/transactionArgument.ts, view and build APIs
• Pattern: TYPESCRIPT_SDK.md
• Related: ts-sdk-view-and-query, ts-sdk-transactions, use-ts-sdk