buf.lastindexOf(value[,byteOffset][,encoding]) function in Node.js

In this article, we will discuss the buf.lastIndexOf(value[, byteOffset][, encoding]) method in Node.js with its syntax, parameters, and examples.

What is the buf.lastIndexOf(value[, byteOffset][, encoding]) method in Node.js?

The buf.lastIndexOf(value[, byteOffset][, encoding]) method is used to obtain the last occurrence of value within the buffer object. The value to find within the buffer can be an integer (byte), string, and buffer. If the value is given as a string, the parameter encoding (such as "utf8" or "ASCII") is utilised, and the optional byte offset is used to indicate where the search should begin, which is by default from the end. This function returns the index of the last occurrence of the value, and -1 is returned if it cannot be found. It works similarly to String.prototype.lastIndexOf() but is specifically designed for reverse searches on binary data.

Syntax:

It has the following syntax:

Parameters:

1. Value(Required): It may be a String, buffer or a number(which represents a byte).
2. Byteoffset (Optional): The search will start from the index of the buffer. If not specified, the end of the buffer or the highest index is used. The way to interpret negative integers is to count backward from the end of the buffer.
3. Encoding (Optional): For comparison, if the value is a string, the encoding specifies how the string should be converted into bytes. While the default encoding is 'utf8', others like 'ascii', 'base64', and 'hex' can be used.

Return Value:

The function returns the index of the most recent value that appeared in the buffer.

If no value is found, -1 is returned by the function.

Key Features:

Several key features of this function are as follows:

• Reverse Search: This function identifies the final instance of a given value by moving backward from the end of a buffer.
• Multiple types of values: Strings, bytes, and buffers are some of the basic types that can be utilized as the search key.
• ByteOffset: It is an optional parameter designed to accept a starting index position for the search, with the default being the end of the buffer.
• Support for Encoding: There are cases in which the value is a string, in which case encoding, such as "utf8" and "ASCII", may be used to describe the byte representation.
• Return Value: If the search term is not found, '-1' will be returned; otherwise, it returns the position of the most recent occurrence of the search value.
• Binary data: Since Binary Data Search employs buffer objects, this method is suitable for performing searches in binary data.

Example 1:

Let us take an example to illustrate the buf.lastIndexOf(value[, byteOffset][, encoding]) method in Node.js.

Output:

 31 0 40 20 

Explanation:

• In this example, the function searches for strings and byte values.
• The effect of providing a byteOffset and case sensitivity is illustrated.

Example 2:

Let us take another example to illustrate the buf.lastIndexOf(value[, byteOffset][, encoding]) method in Node.js. If the value or string is not present in the buffer:

Output:

 -1 25 -1 24 

Explanation:

• The function returns -1 for the values, which are not found inside the buffer.
• As value gives the range of search owing to the byteOffset, if a value is beyond that range -1 is returned.

Conclusion:

In Node.js, the function buf.lastIndexOf(value[, byteOffset][, encoding]) function will enable working with a buffer through reverse search. It will search for text, byte-values, and other buffers. With so many encodings and an optional byteOffset, the place and manner of the search may be controlled. It is a sure way to determine the presence or absence of data, particularly when binary or textual data processing is underway, because it will return -1 if the value cannot be found.