JavaScript Split, Split string by last DOT "."

var str = "filename.to.split.pdf"
var arr = str.split(".");      // Split the string using dot as separator
var lastVal = arr.pop();       // Get last element
var firstVal = arr.join(".");  // Re-join the remaining substrings, using dot as separator

console.log(firstVal + " and " + lastVal);  //Printing result

In order to split a string matching only the last character like described you need to use regex "lookahead".

This simple example works for your case:

var array = '123.2345.34'.split(/\.(?=[^\.]+$)/);
console.log(array);

Example with destructuring assignment (Ecmascript 2015)

const input = 'jquery.somePlugin.v1.6.3.js';
const [pluginName, fileExtension] = input.split(/\.(?=[^\.]+$)/);
console.log(pluginName, fileExtension);

However using either slice or substring with lastIndexOf also works, and albeit less elegant it's much faster:

var input = 'jquery.somePlugin.v1.6.3.js';
var period = input.lastIndexOf('.');
var pluginName = input.substring(0, period);
var fileExtension = input.substring(period + 1);
console.log(pluginName, fileExtension);