Remove all items after an index

Use Array.length to set a new size for an array, which is faster than Array.splice to mutate:

var array = ['mario','luigi','kong', 1, 3, 6, 8];
array.length=2;
alert(array); // shows "mario,luigi";

Why is it faster? Because .splice has to create a new array containing all the removed items, whereas .length creates nothing and "returns" a number instead of a new array.

To address .splice usage, you can feed it a negative index, along with a huge number to chop off the end of an array:

var array = ['mario','luigi','kong'];
array.splice(-1, 9e9); 
alert(array); // shows "mario,luigi";

Though assigning a shorter value to the array length(as @dandavis said) is the fastest and simplest way to remove trailing element from an array, you can also do that using a similar method like splice which is known as slice. Like following:

array = ['mario', 'luigi', 'kong'];

array = array.slice(0, 2); //Need to assign it to the same or another variable

console.log(array); //["mario", "luigi"]

As you can see you need to store the returned value from slice method. To understand 'why', here are the major distinction between slice and splice method:

• The splice() method returns the removed item(s) in an array and slice() method returns the selected element(s) in an array, as a new array object.
• The splice() method changes the original array and slice() method doesn’t change the original array.

To remove all items after an index:

var array = ['mario','luigi','kong'],
index = 1; // your index here
array.splice(index + 1, array.length - (index + 1) );
// 3 - (1+1) = 1
// 1 is the remaining number of element(s) in array
// hence, splice 1 after index

Result:

['mario', 'luigi']

You need to +1 since splice starts removing at the index.