JavaScript class for reading files line by line in HTML5 apps

LineReader.js

/*
Written by Peter O.

Any copyright to this work is released to the Public Domain.
In case this is not possible, this work is also
licensed under Creative Commons Zero (CC0):
https://creativecommons.org/publicdomain/zero/1.0/

*/

function LineReader(file){
 this.file=file;
 this.reader=new FileReader();
 this.offset=0;
 this.currentLine="";
 this.bufferOffset=0;
 this.lastBuffer=null;
 this.callback=null;
 this.omittedCR=false;
 this.sawCR=false;
 this.endCallback=null;
 this.decodeOptions={"stream":true}
 this.decoder=new TextDecoder("utf-8",{"ignoreBOM":true});
 this.reader.addEventListener("load",this._viewLoaded.bind(this));
 this.reader.addEventListener("error",this._error.bind(this));
}
LineReader.prototype._error=function(e){
 throw e;
}
LineReader.prototype._readFromView=function(a,offset){
  for(var i=offset;i<a.length;i++){
   // Treats LF and CRLF as line breaks
   if(a[i]==0x0A){
    // Line feed read
    var lineEnd=(this.sawCR ? i-1 : i);
    if(lineEnd>0){
     this.currentLine+=this.decoder.decode(a.slice(this.bufferOffset,lineEnd),this.decodeOptions);
    }
    if(this.callback)this.callback(this.currentLine)
    this.decoder.decode(new Uint8Array([]))
    this.currentLine="";
    this.sawCR=false;
    this.bufferOffset=i+1;
    this.lastBuffer=a;
   } else if(a[i]==0x0D){
    if(this.omittedCR)this.currentLine+="\r";
    this.sawCR=true;
   } else if(this.sawCR){
    if(this.omittedCR)this.currentLine+="\r";
    this.sawCR=false;
   }
   this.omittedCR=false;
  }
  if(this.bufferOffset!=a.length){
   // Decode the end of the line if no current line was reached
    var lineEnd=(this.sawCR ? a.length-1 : a.length);
    if(lineEnd>0){
     this.currentLine+=this.decoder.decode(a.slice(this.bufferOffset,lineEnd),this.decodeOptions);
    }
    this.omittedCR=this.sawCR;
  }
}
LineReader.prototype._viewLoaded=function(){
 var a=new Uint8Array(this.reader.result);
 if(a.length>0){
  this.bufferOffset=0;
  this._readFromView(a,0);
  this.offset+=a.length;
  var s=this.file.slice(this.offset,this.offset+256);
  this.reader.readAsArrayBuffer(s);
 } else {
  if(this.callback && this.currentLine.length>0){
   this.callback(this.currentLine);
  }
  this.decoder.decode(new Uint8Array([]))
  this.currentLine="";
  this.sawCR=false;
  if(this.endCallback){
    this.endCallback();
  }
 }
}
LineReader.prototype.readLines=function(callback,endCallback){
  this.callback=callback;
  this.endCallback=endCallback;
  var s=this.file.slice(this.offset,this.offset+8192);
  this.reader.readAsArrayBuffer(s);
}
if(typeof exports!="undefined")exports.LineReader=LineReader;