Node.js - Buffer.readUInt8() Method

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The Node.JS Buffer.readUInt8() method helps to read a 8-bit unsigned number at a given offset from the current buffer object. With 8-bit the range of value for unsigned is 0 to 255. For signed it is -128 to 127.

Syntax

Following is the syntax of the Node.JS Buffer.readUInt8() Method −

buf.readUInt8([offset])

Parameters

• offset − The offset that indicates the position to start reading. The offset is greater than or equal to 0 and also less than or equal to buffer.length-1. The default value is 0.

Return value

This method returns the 8-bit unsigned integer number from the current buffer at the given offset.

Example

To create a buffer, we are going to make use of NodeJS Buffer.from() method −

const buffer = Buffer.from([1, 2 ,3, 4, 5, 6, 7, 8]);
console.log("buffer length is ", buffer.length);  
console.log("Reading integer at offset 5:", buffer.readUInt8(5));

Output

The offset that can be used is length of buffer −1. So in the above example we can use 0 to 7. We have used offset as 5 so an 8-bit unsigned integer at the 5th position will be returned. If the offset given is greater than 7 it will give an error ERR_OUT_OF_RANGE.

buffer length is  8
Reading integer at offset 5: 6

Example

In the example below will make use of the string in buffer.from().

const buffer = Buffer.from("Hello World");
console.log("buffer length is ", buffer.length);  
console.log("Reading integer at offset 2:", buffer.readUInt8(2));

Output

In the above example, the length of the buffer created is 11. So for offset, we can use the value from 0 to 10.

buffer length is 11
Reading integer at offset 2: 108

Example

This example will check on the error if the offset is greater than the buffer.length-1. Let us create a buffer having a length of 8 and with that, you can offset the value as 0 to 7.

const buffer = Buffer.from([1, 2 ,3, 4, 5, 6, 7, 8]);
console.log("buffer length is ", buffer.length);  
console.log("Reading at big integer at offset 8:", buffer.readUInt8(8));

Output

Since we have used an offset greater than 7 in the above program, it will throw an error as shown below −

buffer length is 8
internal/buffer.js:58
   throw new ERR_OUT_OF_RANGE(type || 'offset',
   ^
   
RangeError [ERR_OUT_OF_RANGE]: The value of "offset" is out of range. It must be >= 0 and <= 7. Received 8
   at boundsError (internal/buffer.js:58:9)
   at Buffer.readUInt8 (internal/buffer.js:148:5)
   at Object.<anonymous> (C:\nodejsProject\src\testbuffer.js:3:59)
   at Module._compile (internal/modules/cjs/loader.js:816:30)
   at Object.Module._extensions..js (internal/modules/cjs/loader.js:827:10)
   at Module.load (internal/modules/cjs/loader.js:685:32)
   at Function.Module._load (internal/modules/cjs/loader.js:620:12)
   at Function.Module.runMain (internal/modules/cjs/loader.js:877:12)
   at internal/main/run_main_module.js:21:11