Format number for only 2 digits

To round to the nearest number, the simplest is to use toFixed :

var x = 4.499999999999999;
var y = x.toFixed(1);

document.querySelector("body").innerHTML += "<p>" + y + "</p>";

Now to round down, you need to use the floor function and some more calculation:

var x = 4.499999999999999;
var y = Math.floor(10*x)/10;

document.querySelector("body").innerHTML += "<p>" + y + "</p>";

Note that the first method converts the number to a string, while the second method only performs a calculation with it (the result remains a number). I can not think of an example, but it's possible that even after the calculation the number is not as accurate as you intended (given the limitations of floating-point representation) - so it's advisable to use toFixed too in the result if you use method 2.

If the number is in string format and you want to round to string you have two possibilities: