A line by line async file reader for the browser
npm install browser-line-readerThis project addresses the lack of asynchronous, promise aware, typescript based file reader solutions specifically
crafted for the browser.
This module reads a File object, using the standard FileReader, one line at a time.
In order to achieve this, the file is subject to multiple reads, in 'chunks', which can contain any number of lines.
The advantage of this method is that there is no need for the entire file to be stored in browser memory,
and lines can be processed and then discarded.
This is especially useful when reading in large files spanning many hundreds of megabytes.
npm install browser-line-reader --save
Usage
The following types are used in the type signatures below:typescript
interface Options {
encoding?: string;
}type LineReaderCallback = (line: string) => void;
`To get started, import the
class as a default export.`typescript
import LineReader from 'browser-line-reader';
`$3
Type: The
class constructor accepting the File object to read.
`typescript
const myFile: File = new File(['My name is...'], 'SlimShady');
const lineReader: LineReader = new LineReader(myFile);
`$3
Type: Read all the lines of a file, one by one.
Accepts a callback with one parameter of type
, which is the line just read.
Returns a promise containing the total number of lines read.
Throws an error passed through from the internal FileReader.prototype.onerror event.`typescript
lineReader.readLines((line: string) => {
console.log(line);
}).then((numLinesRead: number) => {
console.log(Finished and read ${numLinesRead} lines);
}).catch((err) => {
console.log(err);
});
`$3
Type: Read the first
lines of a file of k lines, or all lines if n > k or n < 0.
Return and exceptions are identical to Linereader.prototype.readLines.`typescript
lineReader.readNLines(10, (line: string) => {
console.log(line);
});
``- Support for different kinds of line separators
- Support for separate read header action
- Efficiency optimisations
- Benchmarking against standard FileReader API
- Add contributing guidelines
Please suggest or implement these or any other features you feel are missing.