Javascript：分页

Question

I have to get from and to indices of the records.

Ideas would be appreciated. For instance, if:

data = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]
records_per_page = 4

the page numbers would be 1,2,3,4,5 (last page having one record).

I need to get the indices based on the page numbers.

For Example I click Page 1, it should give me 0 and 3 so that I send this from and to indices to server and then it returns me values [1,2,3,4]

If I click Page 2, it should give me 4 and 7 so that server returns me values [5,6,7,8]

function(total, page_no){ 
 // Need to return the indices of the records
 return [from,to]
}

Answer 1

You could chunk the array down into only the first and last indices of every x amount of elements:

 var data = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17] const size = 4 const getIndices = (d, p) => p && p <= Math.ceil(d.length / size) && d.reduce((a, o, i) => { const c = Math.floor(i / size); a[c] = [].concat((a[c] && a[c][0] || []), o); if(a[c].length === 1) a[c] = [a[c][0], a[c][0]] return a }, [])[p - 1].map(i => --i) for(var i = 1; i < Math.ceil(data.length / size) + 1; i++) { console.log(getIndices(data, i)) }

EDIT: I just realised this is a simple maths problem. Use this code instead:

 var length = 17 const size = 4 const getIndices = (p, s, l) => p && p <= Math.ceil(l / s) && [s * (p - 1), s * p > l - 1 ? l - 1 : s * p - 1] for(var i = 1; i < Math.ceil(length / size) + 1; i++) { console.log(getIndices(i, size, length)) }

Second edit:

 var length = 17 const size = 4 const getIndices = (p, s, l) => +p && +p <= Math.ceil(l / s) && s * --p for(var i = 1; i < Math.ceil(length / size) + 1; i++) { console.log(getIndices(i, size, length)) }

Note, this function could be a lot shorter, but I have added 2 error checks: p checks to see if p actually exists. && chains all of the conditions to make sure all of them are met. p <= Math.ceil(d.length / size) checks whether p is bigger than the max amount of pages. The next part is the actual logic, returning the page start (and end) indices.