readable and marginally commented version of http://scripts.shpg.org/TableThis.js

tablethis-xp.js

var $$;
if(!Array.prototype.forEach){
  Array.prototype.forEach = function(fun){
    var len=this.length;
    if(typeof fun!=="function"){
	  throw new TypeError();
	}

	var thisp = arguments[1];

	for(var i=0;i<len;i++){
	  if(i in this){
	    fun.call(thisp,this[i],i,this);
	  }
	}
  };
}

if(typeof String.prototype.trim!=='function'){
  String.prototype.trim = function(){
    return this.replace(/^\s+|\s+$/g,'');
  }
}


function init(){
  $$=jQuery;

  //MOUSEENTER CODE FOR ALL TABLES
  $$('table').mouseenter(
    function(){

      //store a few variables to be accessed within the closure without getting confused by "this"
      var pos=$$(this).offset();
      var width=$$(this).width();
      var height=$$(this).height();
      $$(this).css("cursor","pointer");

      //create a new div, and make it a 'table-overlay'
      //NB:  Jquery passed HTML code creates a new element on the DOM
      var tableOverlay=$$("<div></div>").addClass('table-overlay');
      tableOverlay.offset(pos).width(width).height(height);
      tableOverlay.css(
        { "position":"absolute",
          "background":"#000",
          "background":"rgba(0,0,0,0.4)",
          "z-index":100000,
          "pointer-events":"none",
          "cursor":"pointer",
          "display":"table"}
        );

      var tableText=$$("<div></div>").addClass('table-text');
      tableText.text('Click to download table as CSV file').css(
        { "color":"white",
          "pointer-events":"none",
          "display":"table-cell",
          "text-align":"center",
          "vertical-align":"middle",
          "font-size":"26px",
          "font-family":"Arial",
          "font-weight":"800"}
        );

      tableOverlay=tableOverlay.append(tableText);
      $$('body').append(tableOverlay);
    });

  //MOUSELEAVE CODE FOR ALL TABLES
  //it suffices to destroy the table-overlay object
  $$('table').mouseleave(
    function(){
      $$('div.table-overlay').remove();
    });

  //CLICK CODE:  BASICALLY FORWARD THIS TO THE 'tableData' function which gets defined later...
  $$('table').click(
    function(){
      var table=$$(this);
      tableData(table);
  })
}

function csvDownload(str,utf){
  var a=document.createElement('a');
  if(utf)
    {a.href='data:text/csv;charset=utf-16,'+ str;}
  else {a.href='data:text/csv,'+ str;}

  a.target='_blank';
  a.download="tabledownload.csv";
  document.body.appendChild(a);
  a.click();
}


function utf16Checker(str){
  var re=/%u\d/;
  var string=escape(str);
  var res=string.search(re);
  return(res!==-1);
}


function tableData(table){
  var tr=table.find('> tr, > tbody > tr');
  var tableString="";
  var tableData = $$.map(tr,function(tr){
    var row=[$$.map($$(tr).children(),function(td){return $$(td).text();})];
    return row;}
  );

  tableData.forEach(function(entry){
    entry.forEach(function(i){
      var re=new RegExp(" ","g"), rdq=new RegExp('"',"g"), rlb=new RegExp("\n","g");
      i=i.trim();
      //URL escaping
      i=i.replace(re,"%20");
      i=i.replace(rdq,'\"');
      i=i.replace(rlb,'%0D');
      tableString+='"'+ i+'",';}
    )

    tableString=tableString.substring(0,tableString.length- 1);
    tableString+="%0A";}
  );

  if(utf16Checker(tableString)){
    csvDownload(tableString,true);
    alert("NOTE: Because this table contains special characters, the data has been downloaded in UTF-16 format. \n\nThis may cause compatibility issues with some spreadsheet programs.");
  }else{csvDownload(tableString,false);}
}

//initialize this baby
init();