---
tags: Client library
order: 7
---

# OBI Module of Bandchain.js

Oracle Binary Encoding (OBI) is the standard way to serialized and deserialize binary data in the BandChain ecosystem. This module provides the functionality to serialize data. [More details](TODO: add links).

Bandchain.js provide a class named `Obi` to help encode/decode binary data using OBI encoding. Here is the usage of the class.

## Constructor

- **schema** `string` - A string of OBI schema, including input and output schemas.

### Example

import { Obi } from "@bandprotocol/bandchain.js";

const obi = new Obi(
  "{symbol:string,px: u64, in: {a: u8, b: u8}, tb: [string]} / string"
);

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## `encodeInput(value)`

Encode the value based on given OBI input schema

### Parameter

- value `any` - A value to be encoded. can be any type of data.

### Return

- `Buffer` - An encoded value

### Example

import { Obi } from "@bandprotocol/bandchain.js";

const obi = new Obi(
  "{symbol:string,px: u64, in: {a: u8, b: u8}, tb: [string]} / string"
);
const testInput = { symbol: "BTC", px: 9000, in: { a: 1, b: 2 }, tb: ["a","b"] };
console.log(obi.encodeInput(testInput).toString('hex'));

### Result

00000003425443000000000000232801020000000200000001610000000162

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## `encodeOutput(value)`

Encode the value based on OBI output schema

### Parameter

- value `any` - The value to be encoded

### Return

- `Buffer` - An encoded value

### Example

import { Obi } from "@bandprotocol/bandchain.js";

const obi = new Obi(
  "{symbol:string,px: u64, in: {a: u8, b: u8}, tb: [string]} / string"
);
const testOutput = "test";
console.log(obi.encodeOutput(testOutput).toString('hex'));

### Result

0000000474657374

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## `decodeInput(buff)`

Decode the value based on given OBI input schema

### Parameter

- value `Buffer` - The value to be decoded

### Return

- `any` - A decoded value

### Exceptions

| Type | Description |
| ----------- | ---------------------------------------------- |
| DecodeError | Not all data is consumed after decoding output |

### Example

import { Obi } from "@bandprotocol/bandchain.js";

const obi = new Obi(
  "{symbol:string,px: u64, in: {a: u8, b: u8}, tb: [string]} / string"
);
console.log(
  obi.decodeInput(Buffer.from("00000003425443000000000000232801020000000200000001610000000162", "hex"))
);

### Result

{ symbol: 'BTC', px: 9000n, in: { a: 1n, b: 2n }, tb: [ 'a', 'b' ] }

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## `decodeOutput(buff)`

Decode the output value by using output schema

### Parameter

- value `Buffer` - The value to be decoded

### Return

- `any` - A decoded value

### Exceptions

| Type | Description |
| ----------- | ---------------------------------------------- |
| DecodeError | Not all data is consumed after decoding output |

### Example

import { Obi } from "@bandprotocol/bandchain.js";

const obi = new Obi(
  "{symbol:string,px: u64, in: {a: u8, b: u8}, tb: [string]} / string"
);
console.log(obi.decodeOutput(Buffer.from("0000000474657374", "hex")));

### Result

test

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