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How to use the buf.indexOf() function in Node.js

Ayesha Naeem

The buf.indexof() function takes a value and returns the index of where that value first occured in the buffer.

Prototype

Parameters and return value

The buf.indexOf() function accepts three parameters:

  • value: The buf.indexOf() function returns the first occurrence of value in the buffer (buf). value can be of type string, buffer,integer, and Uint8Array.
  • byteoffset: Indicates where to begin the search in the buffer (buf), and is set to 0 by default. If byteoffset is negative, it is set to the end of the buffer (buf). byteoffset is of type integer.
  • encoding: Determines the binary representation of the value if it is of type string. encoding is set to utf-8 by default.

The buf.indexOf() function returns an integer indicating the index at which the value lies in the buffer (buf), and returns -1 if the value does not exist in buf.

Note: The program will throw a TypeError if value is not a string, buffer, or integer.

Examples

The following code demonstrates how to use the Buffer.indexOf() function in Node.js.

// create a buffer
var buf = Buffer.from("Educative.io")
//call the indexOf() function
console.log(buf.indexOf('e'))
// set the offset to the 4th byte
console.log(buf.indexOf('i',4))
//input the ascii value of c
console.log(buf.indexOf(99))
//input an out of range number. 97 is the ascii of a.
console.log(buf.indexOf(97+256))
//input the value as a buffer
console.log(buf.indexOf(Buffer.from('tive.io')))

The above program applies the buf.indexOf() function on values of type string, buffer, and integer.

  • The program calls the indexOf() function on a buffer created with a string and obtains the indexes of the string’s characters in the buffer.
  • The program then inputs an integeris treated as an ASCII value, and the index of the corresponding character is returned.
  • When an out-of-range ASCII value is input to the function, the program truncates the value and returns the character corresponding to the truncated value.
  • The program uses another buffer to test the indexOf() function and returns the index from where the other buffer starts.

Note: If value is a number outside of the range 0-255, the number is converted into a valid byte integer. If byteoffset is not a valid byte, it is converted into a valid byte. The entire buffer is searched if byteoffset is converted to 0 or NaN.

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