How to create a buffer space and write to it in Node.js?

Published September 21, 2020

Create buffer space

To create buffer space we can use the alloc() method in the global Buffer class in Node.js.

  • The method takes the number of bytes (integer) to allocate as the first argument.
  • The method returns a buffer object.

Let's allocate a buffer space of 10 bytes.

// allocate 10 bytes of buffer space
const buff = Buffer.alloc(10);

// display buff contents
console.log(buff); // <Buffer 00 00 00 00 00 00 00 00 00 00>

To initialize the bytes with other than 0, you can pass that integer or string as the second argument like this,

// allocate 10 bytes of buffer space
// allocate with integer 1
const buff = Buffer.alloc(10, 1);

// display buff contents
console.log(buff); // <Buffer 01 01 01 01 01 01 01 01 01 01>

Write to Buffer

To write to a buffer space we can use the write() method in the Buffer object.

  • The method accepts a string as the first argument to write.
// allocate 10 bytes of buffer space
const buff = Buffer.alloc(10);

// write to buffer
const bytesWrote = buff.write("John Doe");

console.log(bytesWrote); // 8
console.log(buff); // Raw Buffer: <Buffer 4a 6f 68 6e 20 44 6f 65 00 00>
console.log(buff.toString()); // String: John Doe

We can use the toString() method in the buff object to convert a raw buffer to string.

We can also define the starting point where it needs to write to the buffer.

For example, if we want to write to buffer after 2 bytes we can pass that as the second argument to the write() method.

// allocate 10 bytes of buffer space
const buff = Buffer.alloc(10);

// write to buffer
// after 2 bytes
const bytesWrote = buff.write("John Doe", 2);

console.log(bytesWrote); // 8
console.log(buff); // Raw Buffer: <Buffer 00 00 4a 6f 68 6e 20 44 6f 65>
console.log(buff.toString()); // String: John Doe

If you look closely into the contents inside the buff variable you can see that the first 2 bytes are 00 00 which means we started writing into the buffer after 2 bytes.

See this example live in repl.it.

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