Buffer.lastIndexOf method | Node.js buffer module | Bun

Buffer.lastIndexOf method | Node.js buffer module | BunBuildDocsReferenceGuidesBlogDiscord/node:buffer/Buffer/lastIndexOfMlastIndexOf

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method

buffer.Buffer.lastIndexOflastIndexOf(value: string | number | Uint8ArrayArrayBufferLike>,byteOffset?: number,encoding?: BufferEncoding): number;Identical 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.

@param valueWhat to search for.

@param byteOffsetWhere to begin searching in buf. If negative, then offset is calculated from the end of buf.

@param encodingIf value is a string, this is the encoding used to determine the binary representation of the string that will be searched for in buf.

@returnsThe index of the last occurrence of value in buf, or -1 if buf does not contain value.

lastIndexOf(value: string | number | Uint8ArrayArrayBufferLike>,encoding: BufferEncoding): number;Referenced typesclass Uint8ArrayTArrayBuffer extends ArrayBufferLike = ArrayBufferLike>A typed array of 8-bit unsigned integer values. The contents are initialized to 0. If the requested number of bytes could not be allocated an exception is raised.

readonly [Symbol.toStringTag]: 'Uint8Array'readonly buffer: TArrayBufferThe ArrayBuffer instance referenced by the array.

readonly byteLength: numberThe length in bytes of the array.

readonly byteOffset: numberThe offset in bytes of the array.

readonly BYTES_PER_ELEMENT: numberThe size in bytes of each element in the array.

readonly length: numberThe length of the array.

[Symbol.iterator](): ArrayIteratornumber>;at(index: number): undefined | number;Returns the item located at the specified index.

@param indexThe zero-based index of the desired code unit. A negative index will count back from the last item.

copyWithin(target: number,start: number,end?: number): this;Returns the this object after copying a section of the array identified by start and end to the same array starting at position target

@param targetIf target is negative, it is treated as length+target where length is the length of the array.

@param startIf start is negative, it is treated as length+start. If end is negative, it is treated as length+end.

@param endIf not specified, length of the this object is used as its default value.

entries(): ArrayIterator[number, number]>;Returns an array of key, value pairs for every entry in the array

every(predicate: (value: number, index: number, array: this) => unknown,thisArg?: any): boolean;Determines whether all the members of an array satisfy the specified test.

@param predicateA function that accepts up to three arguments. The every method calls the predicate function for each element in the array until the predicate returns a value which is coercible to the Boolean value false, or until the end of the array.

@param thisArgAn object to which the this keyword can refer in the predicate function. If thisArg is omitted, undefined is used as the this value.

fill(value: number,start?: number,end?: number): this;Changes all array elements from start to end index to a static value and returns the modified array

@param valuevalue to fill array section with

@param startindex to start filling the array at. If start is negative, it is treated as length+start where length is the length of the array.

@param endindex to stop filling the array at. If end is negative, it is treated as length+end.

filter(predicate: (value: number, index: number, array: this) => any,thisArg?: any): Uint8ArrayArrayBuffer>;Returns the elements of an array that meet the condition specified in a callback function.

@param predicateA function that accepts up to three arguments. The filter method calls the predicate function one time for each element in the array.

@param thisArgAn object to which the this keyword can refer in the predicate function. If thisArg is omitted, undefined is used as the this value.

find(predicate: (value: number, index: number, obj: this) => boolean,thisArg?: any): undefined | number;Returns the value of the first element in the array where predicate is true, and undefined otherwise.

@param predicatefind calls predicate once for each element of the array, in ascending order, until it finds one where predicate returns true. If such an element is found, find immediately returns that element value. Otherwise, find returns undefined.

@param thisArgIf provided, it will be used as the this value for each invocation of predicate. If it is not provided, undefined is used instead.

findIndex(predicate: (value: number, index: number, obj: this) => boolean,thisArg?: any): number;Returns the index of the first element in the array where predicate is true, and -1 otherwise.

@param predicatefind calls predicate once for each element of the array, in ascending order, until it finds one where predicate returns true. If such an element is found, findIndex immediately returns that element index. Otherwise, findIndex returns -1.

@param thisArgIf provided, it will be used as the this value for each invocation of predicate. If it is not provided, undefined is used instead.

findLastS extends number>(predicate: (value: number, index: number, array: this) => value is S,thisArg?: any): undefined | S;Returns the value of the last element in the array where predicate is true, and undefined otherwise.

@param predicatefindLast calls predicate once for each element of the array, in descending order, until it finds one where predicate returns true. If such an element is found, findLast immediately returns that element value. Otherwise, findLast returns undefined.

@param thisArgIf provided, it will be used as the this value for each invocation of predicate. If it is not provided, undefined is used instead.

findLast(predicate: (value: number, index: number, array: this) => unknown,thisArg?: any): undefined | number;findLastIndex(predicate: (value: number, index: number, array: this) => unknown,thisArg?: any): number;Returns the index of the last element in the array where predicate is true, and -1 otherwise.

@param predicatefindLastIndex calls predicate once for each element of the array, in descending order, until it finds one where predicate returns true. If such an element is found, findLastIndex immediately returns that element index. Otherwise, findLastIndex returns -1.

@param thisArgIf provided, it will be used as the this value for each invocation of predicate. If it is not provided, undefined is used instead.

forEach(callbackfn: (value: number, index: number, array: this) => void,thisArg?: any): void;Performs the specified action for each element in an array.

@param callbackfnA function that accepts up to three arguments. forEach calls the callbackfn function one time for each element in the array.

@param thisArgAn object to which the this keyword can refer in the callbackfn function. If thisArg is omitted, undefined is used as the this value.

includes(searchElement: number,fromIndex?: number): boolean;Determines whether an array includes a certain element, returning true or false as appropriate.

@param searchElementThe element to search for.

@param fromIndexThe position in this array at which to begin searching for searchElement.

indexOf(searchElement: number,fromIndex?: number): number;Returns the index of the first occurrence of a value in an array.

@param searchElementThe value to locate in the array.

@param fromIndexThe array index at which to begin the search. If fromIndex is omitted, the search starts at index 0.

join(separator?: string): string;Adds all the elements of an array separated by the specified separator string.

@param separatorA string used to separate one element of an array from the next in the resulting String. If omitted, the array elements are separated with a comma.

keys(): ArrayIteratornumber>;Returns an list of keys in the array

lastIndexOf(searchElement: number,fromIndex?: number): number;Returns the index of the last occurrence of a value in an array.

@param searchElementThe value to locate in the array.

@param fromIndexThe array index at which to begin the search. If fromIndex is omitted, the search starts at index 0.

map(callbackfn: (value: number, index: number, array: this) => number,thisArg?: any): Uint8ArrayArrayBuffer>;Calls a defined callback function on each element of an array, and returns an array that contains the results.

@param callbackfnA function that accepts up to three arguments. The map method calls the callbackfn function one time for each element in the array.

@param thisArgAn object to which the this keyword can refer in the callbackfn function. If thisArg is omitted, undefined is used as the this value.

reduce(callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: this) => number): number;Calls the specified callback function for all the elements in an array. The return value of the callback function is the accumulated result, and is provided as an argument in the next call to the callback function.

@param callbackfnA function that accepts up to four arguments. The reduce method calls the callbackfn function one time for each element in the array.

reduce(callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: this) => number,initialValue: number): number;reduceU>(callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: this) => U,initialValue: U): U;Calls the specified callback function for all the elements in an array. The return value of the callback function is the accumulated result, and is provided as an argument in the next call to the callback function.

@param callbackfnA function that accepts up to four arguments. The reduce method calls the callbackfn function one time for each element in the array.

@param initialValueIf initialValue is specified, it is used as the initial value to start the accumulation. The first call to the callbackfn function provides this value as an argument instead of an array value.

reduceRight(callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: this) => number): number;Calls the specified callback function for all the elements in an array, in descending order. The return value of the callback function is the accumulated result, and is provided as an argument in the next call to the callback function.

@param callbackfnA function that accepts up to four arguments. The reduceRight method calls the callbackfn function one time for each element in the array.

reduceRight(callbackfn: (previousValue: number, currentValue: number, currentIndex: number, array: this) => number,initialValue: number): number;reduceRightU>(callbackfn: (previousValue: U, currentValue: number, currentIndex: number, array: this) => U,initialValue: U): U;Calls the specified callback function for all the elements in an array, in descending order. The return value of the callback function is the accumulated result, and is provided as an argument in the next call to the callback function.

@param callbackfnA function that accepts up to four arguments. The reduceRight method calls the callbackfn function one time for each element in the array.

@param initialValueIf initialValue is specified, it is used as the initial value to start the accumulation. The first call to the callbackfn function provides this value as an argument instead of an array value.

reverse(): this;Reverses the elements in an Array.

set(array: ArrayLikenumber>,offset?: number): void;Sets a value or an array of values.

@param arrayA typed or untyped array of values to set.

@param offsetThe index in the current array at which the values are to be written.

setFromBase64(base64: string,offset?: number): { read: number; written: number };Set the contents of the Uint8Array from a base64 encoded string

@param base64The base64 encoded string to decode into the array

@param offsetOptional starting index to begin setting the decoded bytes (default: 0)

setFromHex(hex: string): { read: number; written: number };Set the contents of the Uint8Array from a hex encoded string

@param hexThe hex encoded string to decode into the array. The string must have an even number of characters, be valid hexadecimal characters and contain no whitespace.

slice(start?: number,end?: number): Uint8ArrayArrayBuffer>;Returns a section of an array.

@param startThe beginning of the specified portion of the array.

@param endThe end of the specified portion of the array. This is exclusive of the element at the index 'end'.

some(predicate: (value: number, index: number, array: this) => unknown,thisArg?: any): boolean;Determines whether the specified callback function returns true for any element of an array.

@param predicateA function that accepts up to three arguments. The some method calls the predicate function for each element in the array until the predicate returns a value which is coercible to the Boolean value true, or until the end of the array.

@param thisArgAn object to which the this keyword can refer in the predicate function. If thisArg is omitted, undefined is used as the this value.

sort(compareFn?: (a: number, b: number) => number): this;Sorts an array.

@param compareFnFunction used to determine the order of the elements. It is expected to return a negative value if first argument is less than second argument, zero if they're equal and a positive value otherwise. If omitted, the elements are sorted in ascending order.

[11,2,22,1].sort((a, b) => a - b) subarray(begin?: number,end?: number): Uint8ArrayTArrayBuffer>;Gets a new Uint8Array view of the ArrayBuffer store for this array, referencing the elements at begin, inclusive, up to end, exclusive.

@param beginThe index of the beginning of the array.

@param endThe index of the end of the array.

toBase64(options?: { alphabet: 'base64' | 'base64url'; omitPadding: boolean }): string;Convert the Uint8Array to a base64 encoded string

@returnsThe base64 encoded string representation of the Uint8Array

toHex(): string;Convert the Uint8Array to a hex encoded string

@returnsThe hex encoded string representation of the Uint8Array

toLocaleString(): string;Converts a number to a string by using the current locale.

toLocaleString(locales: string | string[],options?: NumberFormatOptions): string;toReversed(): Uint8ArrayArrayBuffer>;Copies the array and returns the copy with the elements in reverse order.

toSorted(compareFn?: (a: number, b: number) => number): Uint8ArrayArrayBuffer>;Copies and sorts the array.

@param compareFnFunction used to determine the order of the elements. It is expected to return a negative value if the first argument is less than the second argument, zero if they're equal, and a positive value otherwise. If omitted, the elements are sorted in ascending order.

const myNums = Uint8Array.from([11, 2, 22, 1]); myNums.toSorted((a, b) => a - b) // Uint8Array(4) [1, 2, 11, 22] toString(): string;Returns a string representation of an array.

valueOf(): this;Returns the primitive value of the specified object.

values(): ArrayIteratornumber>;Returns an list of values in the array

with(index: number,value: number): Uint8ArrayArrayBuffer>;Copies the array and inserts the given number at the provided index.

@param indexThe index of the value to overwrite. If the index is negative, then it replaces from the end of the array.

@param valueThe value to insert into the copied array.

@returnsA copy of the original array with the inserted value.

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