Node.js Buffer.writeBigUInt64BE() Method

The Buffer.writeBigUInt64BE() method is an inbuilt application programming interface of class Buffer within the Buffer module which is used to writes big endian 64-bits Big integer value to an allocated buffer at the specified offset.
Syntax:

Buffer.writeBigUInt64BE( value, offset )

Parameters: This method accept two parameters as mentioned above and described below: 

• value: This parameter specifies big integer value to be written to the buffer. It should be a valid 64 bits big endian Big integer value. Behavior is undefined when value is anything other than this.
• offset: It specifies the number of bytes to skip before write or simply signify the index in the buffer. The value of offset lies 0 <= offset <= Buffer.length – 8. Its default value is 0.

Return Value: This method returns an unsigned integer value that is the sum of offset and number of bytes written.
Below examples illustrate the use of Buffer.writeBigUInt64BE() method in Node.js:
Example 1:
Filename: index.js

javascript

// Node.js program to demonstrate the
// buffer.writeBigUInt64BE() method
const buf = Buffer.allocUnsafe(8);

// Writing big integer value into buffer
// by using writeBigUInt64BE() method
buf.writeBigUInt64BE(0x01030405060708n, 0);

// Display the buffer
console.log(buf);

Run the index.js file ” 
using the following command: 

node index.js

Output:

<Buffer 00 01 03 04 05 06 07 08>

Example 2:
Filename: index.js

javascript

// Node.js program to demonstrate the
// buffer.writeBigUInt64BE() method
const buf = Buffer.allocUnsafe(8);

// writing big integer value into buffer
// by using writeBigUInt64BE() method
buf.writeBigUInt64BE(0xaa03040506efffn, 0);

// display the buffer
console.log(buf);

Run the index.js file using the following command: 

node index.js

Output:

<Buffer 00 aa 03 04 05 06 ef ff>

Reference: https://nodejs.org/dist/latest-v12.x/docs/api/buffer.html#buffer_buf_writebiguint64be_value_offset