How to easily truncate an array with JavaScript?

(2 years later...) If you're truly looking to truncate an array, you can also use the length attribute:

var stooges = ["Moe", "Larry", "Shemp", "Curly", "Joe"];
stooges.length = 3; // now stooges is ["Moe", "Larry", "Shemp"]

Note: if you assign a length which is longer than current length, undefined array elements are introduced, as shown below.

var stooges = ["Moe", "Larry", "Shemp"];
stooges.length = 5;
alert(typeof stooges[4]); // alerts "undefined"

EDIT:

As @twhitehead mentioned below, the addition of undefined elements can be avoided by doing this:

var stooges = ["Moe", "Larry", "Shemp"];
stooges.length = Math.min(stooges.length, 5); 
alert(stooges.length)// alerts "3"

There is a slice method

let arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
arr = arr.slice(0, 4);
console.log(arr);

Will return the first four elements.

Don't forget to assign it back to your variable if you want to discard the other values.

Note: This is just regular javascript, no need for jquery.