How to count the number of lines of a string in javascript

Another short, potentially more performant than split, solution is:

const lines = (str.match(/\n/g) || '').length + 1

Using a regular expression you can count the number of lines as

 str.split(/\r\n|\r|\n/).length

Alternately you can try split method as below.

var lines = $("#ptest").val().split("\n");  
alert(lines.length);

working solution: http://jsfiddle.net/C8CaX/