pagination calculating

pagination.md

• I want to show result (from-to) at current page. Example: each page having 50 results, will show: 1-50, 51-100, ..., 501-503 final page has not enough 50 results

var resultsPerPage = 50;
var countOfResults = 451; // count of total results  ==> max of page = 10
var countOfCurrentPage = 50; // results of current page, from 1 --> 50
var page = 1; // current page, page begin from 1, not 0
var from = Math.min(countOfResults, 1 + (page - 1) * resultsPerPage); // is `countOfResults` when from page > max of page
var to = (page - 1) * resultsPerPage + countOfCurrentPage;
if (to > countOfResults) to = countOfResults;
console.log(from + '-' + to);

// exmample: countOfResults = 451, resultsPerPage = 50 ==> max of page = 10
// page=1, countOfCurrentPage = 50 ==> 1-50
// page=10, countOfCurrentPage = 1 ==> 451-451
// page=11, countOfCurrentPage = 50 ==> 451-451 // `from` and `to` is `countOfResults`

• Check current page has previous page (newer page) or next page (older page)

var resultsPerPage = 50;
var countOfResults = 451;
var maxOfPages = 1 + Math.floor((countOfResults - 1) / resultsPerPage); // actually don't need to using `Math.floor()` because all variables are integer, `/` will be `integer division` (apply for almost programming language), but not for angular. When I apply the formular without `Math.floor()` in html template (angular), it apply `float division` instead `integer division`, so the formular is not right anymore --> need to using `Math.floor()` if you want apply `integer division` in html angular's template
var page = 3; // current page
var hasPreviousPage = page > 1; // newer page
var hasNextPage = page < maxOfPages; // older page

// example: resultsPerPage = 50
// countOfResults = 0 ==> maxOfPages = 1 + floor((0-1)/50) = 0
// countOfResults = 1 ==> maxOfPages = 1 + floor((1-1)/50) = 1
// countOfResults = 49 ==> maxOfPages = 1 + floor((49-1)/50) = 1
// countOfResults = 50 ==> maxOfPages = 1 + floor((50-1)/50) = 1 
// countOfResults = 51 ==> maxOfPages = 1 + floor((51-1)/50) = 2 
// countOfResults = 450 ==> maxOfPages = 1 + floor((450-1)/50) = 9 
// countOfResults = 451 ==> maxOfPages = 1 + floor((450-1)/50) = 10 

Why using Math.floor()? actually don't need to using Math.floor() because all variables are integer, / will be integer division (apply for almost programming language), but not for angular. When I apply the formular without Math.floor() in html template (angular), it apply float division instead integer division, so the formular is not right anymore --> need to using Math.floor() if you want apply integer division in html angular's template