Shift is at worst O(N) however it can, in specially cases, be implemented as O(1) at the cost of slowing down indexing so your mileage may vary. a copying collector could only copy the used part of an array). Pop is O(1) with a similar caveat to push but the O(N) copy is rarely encountered as it is often folded into garbage collection (e.g. These boundaries are typically logarithmic. Push is O(1), however, in practice it will encounter an O(N) copy costs at engine defined boundaries as the slot array needs to be reallocated. If you don't want to change the array, the slice() method can be used.The ECMA specification does not specify a bounding complexity, however, you can derive one from the specification's algorithms.

You can use it if you are fine with modifying the array. Let us now use all three methods on an array to get the last element and check which method is the fastest let arry = Ĭonsole.timeEnd('array length property') Īs you can see, the pop() method is fastest. This method changes the length of the array. The pop() method pops/removes the last element of an array, and returns it. Providing one index value returns the element at that position & a negative index value calculates the index from the end of the array. The slice() method does not modify the existing array. This method selects the elements starting at the given start index and ends at the given end index excluding the element at the end index. The slice() method returns specific elements from an array, as a new array object. Therefore the last element's index would be array length-1. The reason we are subtracting 1 from the length is, in JavaScript, the array index numbering starts with 0. Subtracting 1 from the length of an array gives the index of the last element of an array using which the last element can be accessed. The length property returns the number of elements in an array.

Array slice in javascript