Node.js hmac.update() Method

The hmac.update() method is an inbuilt method of class HMAC within the crypto module which is used to update the data of hmac object. 

Syntax:

hmac.update(data[, inputEncoding])

Parameters: This method takes the following two parameters:

• data: It can be of string, Buffer, TypedArray, or DataView type. It is the data that is passed to this function.
• inputEncoding: It is an optional parameter. It is the encoding of the data string.

Return Value: This method returns nothing.

Project Setup: Create a new NodeJS project and name it hmac.

mkdir hmac && cd hmac
npm init -y

Now create a .js file in your project root directory and name it index.js

Example 1: 

index.js

// Node.js program to demonstrate the
// crypto hmac.update() method

// Importing crypto module
const { createHmac } = require('crypto')

// Creating and initializing algorithm and password
const algo = 'sha256'
const secret = 'GFG Secret Key'

// Create an HMAC instance
const hmac = createHmac(algo, secret)

// Update the internal state of the hmac object
hmac.update('GeeksForGeeks')

// Perform the final operations
// Return calculated hash
const result = hmac.digest('base64')

// Print the result
console.log(`HMAC hash: ${result}`)

Run the index.js file using the following command:

node index.js

Output:

HMAC hash: yK4+CYVa56w0Ba1g2TdY7cDM68HPXFKb+10FhnRpXFM=

Example 2:

index.js

// Node.js program to demonstrate the
// crypto hmac.update() method

// Defining myfile
const myfile = process.argv[2];

// Includes crypto and fs module
const crypto = require('crypto');
const fs = require('fs');

// Creating and initializing algorithm and password
const algo = 'sha256'
const secret = 'GFG Secret Key'

// Creating Hmac
const hmac = crypto.createHmac(algo, secret);

// Creating read stream
const readfile = fs.createReadStream(myfile);

readfile.on('readable', () => {

  // Calling read method to read data
  const data = readfile.read();

  if (data)

    // Updating
    hmac.update(data);
  else {

    // Perform the final operations
    // Return hash value
    const result = hmac.digest('hex')

    // Display result
    console.log(`HMAC hash value of ${myfile}: ${result}`);
  }
});

Run the index.js file using the following command:

node index.js package.json

Output:

HMAC hash value of package.json: 38f0f975f8964343c24da940188eaeb6bb20842e3c5bf03ccb66773e98beeb73

Reference: https://nodejs.org/api/crypto.html#crypto_hmac_update_data_inputencoding