LineReader
A simple LineReader class, similar to Java's readline() method, written in Typescript (for Node) to read files line-by-line asynchronously and quickly.
Install
# using npm
npm install @dwesley/linereaderUsage
Import
import { LineReader } from "@dwesley/linereader"Example
import { PathLike } from "node:fs"
import { EOL } from "node:os"
import { LineReader } from "@dwesley/linereader"
async function main() {
/** could be any valid path to a readable file */
const PATH: PathLike = "/dev/stdin"
/** the variable value below can be any valid encoding available in the `BufferEncoding` type */
const ENCODING: BufferEncoding = "utf8"
/** `LineReader` instance from the file specified in `PATH` variable */
const lineReader = LineReader.create(PATH, ENCODING)
const output = []
while (lineReader.hasNextLine()) {
const line = await lineReader.nextLine()
output.push(line)
}
console.log(output.join(EOL))
}
main()API
LineReader.create(path: fs.PathLike, encoding: BufferEncoding = "utf8"): LineReaderInstance
The options you can pass are:
| Name | Type | Default | Description |
|---|---|---|---|
| path | string | Buffer | URL |
none | The path or location of your file (required) |
| encoding | 'ascii' | 'utf8' | 'utf-8' | 'utf16le' | 'ucs2' | 'ucs-2' | 'base64' | 'latin1' | 'binary' | 'hex' |
'utf8' |
Character encoding to use on read() operation |
Instance Methods
The methods of LineReader instance you can access are:
| Name | ReturnType | Description |
|---|---|---|
| hasNextLine | boolean |
A function that returns true if there is another line to read, or false if close() has already been called |
| nextLine | Promise |
An async function that reads the next line from the file and returns it. |
| close | void |
A function that closes the LineReader and stops reading lines from the file. |
LineReaderInstance.nextLine<Output>(fn?: (value: string) => Output): Promise<Output | string | undefined>
Asynchronously read next single line of current file stream.
Example:
const lineReader = LineReader.create("./file.txt", "utf-8")
const output = []
while (lineReader.hasNextLine()) {
const line = await lineReader.nextLine()
output.push(line)
}
console.log(output.join(" | "))./file.txt
1111
2222
3333
4444
5555
7777Output:
1111 | 2222 | 3333 | 4444 | 5555 | | 7777
Example with helpers:
/** Helper function that should format the current line */
const helper = (line: string = ""): number[] => {
return line.split(",", 1e5).map((value) => Number.parseInt(value, 10))
}
const output = []
while (lineReader.hasNextLine()) {
/**
* Extended nextLine method for lineReader instance
* This nextLine method uses `helper`function as proxy for return the line content
* Its return type is inherited from helper's return type
*/
const numbers = await lineReader.nextLine(helper)
output.push(numbers.join("-"))
}
console.log(output.join(EOL))./using-helper.txt
1,2,3
4
5,,7Output:
1-2-3
4
5-NaN-7
LineReaderInstance.close(): void
Manually closes the LineReader by calling the close method.
This method will be called automatically on the last nextLine operation.
Example:
const lineReader = LineReader.create("./file.txt")
for (let i = 0; i < 2; i++) {
const line = await lineReader.nextLine()
else console.log(line)
}
if (lineReader.hasNextLine())
lineReader.close()
console.log(await lineReader.nextLine()) // undefined./file.txt
1
2
3
4Output:
1
2
undefined
Contribute
This is open for you to join if you can add value or benefit from this!
License
Feel free to use this library under the conditions of the MIT license.