Add step to slice notation

[Nicolas Lepage]

Description

Add step to the slice notation in order to conform to the ES slice notation: array[start:end:step].

Like start and end, step may be negative.
This doesn't change the fact that start is inclusive and end is exclusive.
When step is negative, start should be greater than end, otherwise slice will be empty.
When step is negative, implicit start becomes length - 1 and implicit (exclusive) end becomes -1.

Examples

Update even elements with step of 2

multiply(
  { nested: { prop: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] } },
  'nested.prop[::2]',
  100,
)
// returns { nested: { prop: [0, 1, 200, 3, 400, 5, 600, 7, 800, 9] } }

Fetch reversed slice with step of -1

get(
  { nested: { prop: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] } },
  'nested.prop[3::-1]'
)
// returns [3, 2, 1, 0]

Clarifying example with negative step

const obj = { nested: { prop: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] } }
get(obj, 'nested.prop[1:3:-1]') // returns []
get(obj, 'nested.prop[3:1:-1]') // returns [3, 2]

[Nicolas Lepage]

Waitin for #327

[Nicolas Lepage]

So I posted an issue on the tc39 proposal to validate this:

Like start and end, step may be negative.
This doesn't change the fact that start is inclusive and end is exclusive.
When step is negative, implicit start becomes length - 1 and implicit (exclusive) end becomes -1.

See tc39/proposal-slice-notation#29