TypedArray.prototype.at()
The at()
method takes an integer value and returns the item at that index, allowing for positive and negative integers. Negative integers count back from the last item in the array.
This is not to suggest there is anything wrong with using the square bracket notation. For example array[0]
would return the first item. However instead of using array.length
for latter items; e.g. array[array.length-1]
for the last item, you can call array.at(-1)
. (See the examples below)
Syntax
at(index)
Parameters
index
-
The index (position) of the array element to be returned. Supports relative indexing from the end of the array when passed a negative index. i.e. If a negative number is used the element returned will be found by counting back from the end of the array.
Return value
The element in the array matching the given index. Returns undefined
if the given index can not be found.
Examples
Return the last value of a typed array
The following example provides a function which returns the last element found in a specified array.
const uint8 = new Uint8Array([1, 2, 4, 7, 11, 18]);
// A function which returns the last item of a given array
function returnLast(arr) {
return arr.at(-1);
}
const lastItem = returnLast(uint8);
console.log(lastItem); // Logs: 18
Comparing methods
Here we compare different ways to select the penultimate (last but one) item of a TypedArray
. Whilst all below methods are valid, it highlights the succinctness and readability of the at()
method.
// Our typed array with values
const uint8 = new Uint8Array([1, 2, 4, 7, 11, 18]);
// Using length property
const lengthWay = uint8[uint8.length-2];
console.log(lengthWay); // Logs: 11
// Using slice() method. Note an array is returned
const sliceWay = uint8.slice(-2, -1);
console.log(sliceWay[0]); // Logs: 11
// Using at() method
const atWay = uint8.at(-2);
console.log(atWay); // Logs: 11
Specifications
Specification |
---|
Relative Indexing Method # sec-%typedarray.prototype%-additions |
Browser compatibility
BCD tables only load in the browser
See also
- Polyfill of
TypedArray.prototype.at
incore-js
- A polyfill for the at() method.
TypedArray.prototype.find()
– return a value based on a given test.TypedArray.prototype.includes()
– test whether a value exists in the array.TypedArray.prototype.indexOf()
– return the index of a given element.