method Buffer.lastIndexOf
#Buffer.lastIndexOf(): numberIdentical to buf.indexOf(), except the last occurrence of value is found
rather than the first occurrence.
import { Buffer } from 'node:buffer';
const buf = Buffer.from('this buffer is a buffer');
console.log(buf.lastIndexOf('this'));
// Prints: 0
console.log(buf.lastIndexOf('buffer'));
// Prints: 17
console.log(buf.lastIndexOf(Buffer.from('buffer')));
// Prints: 17
console.log(buf.lastIndexOf(97));
// Prints: 15 (97 is the decimal ASCII value for 'a')
console.log(buf.lastIndexOf(Buffer.from('yolo')));
// Prints: -1
console.log(buf.lastIndexOf('buffer', 5));
// Prints: 5
console.log(buf.lastIndexOf('buffer', 4));
// Prints: -1
const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'utf16le');
console.log(utf16Buffer.lastIndexOf('\u03a3', undefined, 'utf16le'));
// Prints: 6
console.log(utf16Buffer.lastIndexOf('\u03a3', -5, 'utf16le'));
// Prints: 4
If value is not a string, number, or Buffer, this method will throw a TypeError. If value is a number, it will be coerced to a valid byte value,
an integer between 0 and 255.
If byteOffset is not a number, it will be coerced to a number. Any arguments
that coerce to NaN, like {} or undefined, will search the whole buffer.
This behavior matches String.prototype.lastIndexOf().
import { Buffer } from 'node:buffer';
const b = Buffer.from('abcdef');
// Passing a value that's a number, but not a valid byte.
// Prints: 2, equivalent to searching for 99 or 'c'.
console.log(b.lastIndexOf(99.9));
console.log(b.lastIndexOf(256 + 99));
// Passing a byteOffset that coerces to NaN.
// Prints: 1, searching the whole buffer.
console.log(b.lastIndexOf('b', undefined));
console.log(b.lastIndexOf('b', {}));
// Passing a byteOffset that coerces to 0.
// Prints: -1, equivalent to passing 0.
console.log(b.lastIndexOf('b', null));
console.log(b.lastIndexOf('b', []));
If value is an empty string or empty Buffer, byteOffset will be returned.
Parameters #
#value: string
| number
| Uint8Array What to search for.
#byteOffset: number = buf.length - 1 Where to begin searching in buf. If negative, then offset is calculated from the end of buf.
#encoding: BufferEncoding = 'utf8' If value is a string, this is the encoding used to determine the binary representation of the string that will be searched for in buf.
Return Type #
number The index of the last occurrence of value in buf, or -1 if buf does not contain value.