Slices.JS

This NPM package aims to provide Golang-like array slices to Javascript. Array slices can be very useful when dealing with data partitioned within a flat array.

Introduction

Example, self explanatory code.

const ArraySlice = require('slices.js');

const a = [1, 2, 3, 4, 5, 6, 7];
const b = new ArraySlice(a, 1, -3); // negative indices supported
// last index is -1, first index is -Array.length

// results [2, 3, 4, 5]
b[2] = 3;
// b = [2, 3, 3, 5]
b.reverse();
// b = [5, 3, 3, 2]
a
// [ 1, 5, 3, 3, 2, 6, 7 ]

Functions

Basic properties and methods

Properties and methods unique to the ArraySlice class.

Property: array, ArraySlice

Returns the parent array

const a = [1, 2, 3, 4, 5, 6, 7];
const b = new ArraySlice(a, 1, -3); // negative indices supported

a == b.array // true

Method: subarray , () -> Array

Returns the array slice as an array

b.subarray() // [2, 3, 4, 5] - an Array, NOT an ArraySlice
Array.isArray(b.subarray()) // true

Property: start, Int

Returns the starting index of the slice. Negative indices are converted to their equivalent positive one.

b.start // 1

Property: end, Int

Returns the ending index of the slice Negative indices are converted to their equivalent positive one.

b.end // 5

Method: mutmap, (appliedFunction : Function) -> ArraySlice

Apply and set the value of each value in the slice with a function

a // [1, 2, 3, 4, 5, 6, 7]
b // [2, 3, 4, 5]
b.mutmap(x => x + 1); // [3, 4, 5, 6]
a // [1, 3, 4, 5, 6, 6, 7]

Method: set, (newValues : Array) -> ArraySlice

Set the values of the ArraySlice to corresponding values in an Array

a // [1, 2, 3, 4, 5, 6, 7]
b // [2, 3, 4, 5]
b.set([1, 5, 3, 6]); // [1, 5, 3, 6]
a // [1, 1, 5, 3, 6, 6, 7]

Derived properties and methods

Properties of normal Javascript arrays that are applicable to Array Slices. All methods that act on the slice are destructive. The changes are also reflected in the parent array.

Property: length, Int

Gets the length of the ArraySlice

b // [2, 3, 4, 5]
b.length // 4

Method: copyWithin, (target : Int, start : Int, end : Int) -> ArraySlice

copyWithin is a clone of the corresponding Javascript function. One can think of this as C's memmove function with an array. It copies one portion of the array, specified by start and end, to another part who's starting index is specified by target.

a // [1, 2, 3, 4, 5, 6, 7]
b // [2, 3, 4, 5]
b.copyWithin(2, 0, 2) // [2, 3, 2, 3]
a // [1, 2, 3, 2, 3, 6, 7]

Method: fill, (value : Object) -> ArraySlice

Fills the entire slice with one value.

a // [1, 2, 3, 4, 5, 6, 7]
b // [2, 3, 4, 5]
b.fill(2) // [2, 2, 2, 2]
a // [1, 2, 2, 2, 2, 6, 7]

Method: reverse, () -> ArraySlice

Reverse the entire slice.

a // [1, 2, 3, 4, 5, 6, 7]
b // [2, 3, 4, 5]
b.reverse() // [5, 4, 3, 2]
a // [1, 5, 4, 3, 2, 6, 7]

Method: sort, (comparatorFunction : (a : Object, b : Object) -> Bool) -> ArraySlice

Sorts the slice according to the given comparator function

a // [1, 5, 2, 4, 3, 6, 7]
b // [5, 2, 4, 3]
b.sort((a, b) => a < b) // [2, 3, 4, 5]
a // [1, 2, 3, 4, 5, 6, 7]

Property: constructor, ArraySlice

Returns the ArraySlice constructor

new b.constructor([1, 2, 3]) // [1, 2, 3] is an ArraySlice

Method: valueOf, () -> Array

b // [5, 2, 4, 3]
b.valueOf() // [5, 2, 4, 3] is an Array
Array.isArray(b.valueOf()) // true

Other properties and methods

Nondestructive Array methods like the following:

concat, filter, includes, indexOf, join, lastIndexOf, slice, toString, toLocaleString, entries, every, find, findIndex, forEach, keys, map, reduce, reduceRight, some, values

are not supported; they do not well with the Array Slice model. One can easily use these functions with the subarray method instead. However, a native array will be returned instead of an array slice.

const a = [1, 2, 3, 4, 5, 6, 7];
const b = new ArraySlice(a, 1, -3); 

b.subarray().map(x => x + 1)
// [ 3, 4, 5, 6 ]