javascript coordinate conversions between 900913(3857) - 4326(lat lon)

degrees2meters.js

var degrees2meters = function(lon,lat) {
  var x = lon * 20037508.34 / 180;
  var y = Math.log(Math.tan((90 + lat) * Math.PI / 360)) / (Math.PI / 180);
  y = y * 20037508.34 / 180;
  return [x, y]
}
//test
lon= -77.035974
lat = 38.898717

console.log(degrees2meters(lon,lat))

// should result in: -8575605.398444, 4707174.018280

meters2degrees.js

var meters2degress = function(x,y) {
  var lon = x *  180 / 20037508.34 ;
  //thanks magichim @ github for the correction
  var lat = Math.atan(Math.exp(y * Math.PI / 20037508.34)) * 360 / Math.PI - 90; 
  return [lon, lat]
}
//test
x= -8575605.398444
y = 4707174.018280

console.log(meters2degress(x,y))

//should result in: -77.035974, 38.898717

@AnaKuzina
Heyo again,
I will point 2 situations here.
1-Input values have problem. You are giving input values as text but considering they are numbers. You are getting texts from your inputs. You should either cast'em to Numbers or change the type of your inputs to Number (can be more elegant since you can also set borders and do validations easier).

Try this code:
var degrees2meters = function(lon, lat) {
var x = lon * 20037508.34 / 180;
var y = Math.log(Math.tan((90 + lat) * Math.PI / 360)) / (Math.PI / 180);
y = y * 20037508.34 / 180;
return [x, y]
}

function get3857() {
lat = Number($('#latitude').val());
lon = Number($('#longitude').val());
lon_lat = degrees2meters(lon, lat);

$('#3857_lat').text(lon_lat[1]);
$('#3857_lon').text(lon_lat[0]);
}

2- If it doesn't work, please change the places of lat and lon. %99.999 issues in gis domain comes from confusion on x,y,lat,lon,radian,degree...

@onderaltintas thank you so much! The code works perfect! Also i've changed type of the input fields as you've recommended! Thank you once again, I really appreciate your help!

May I know where did you get a formula for conversion?

May I know where did you get a formula for conversion?

Based on geometric knowledge and you can see the fixes happened in the past by contribution of commenters.

you saved my life, thank you

you saved my life, thank you

I'm glad that I could help. But don't forget that it is just to translate 4326 to 900913(3857) and visa versa. This calculation cannot be used for length measurements because of high error margin.