Simple pagination algorithm

simple-pagination.js

function pagination(c, m) {
  var current = c,
      last = m,
      delta = 2,
      range = [],
      previous = 1;

  range.push(1);
  for (var i = 2; i < last; i++) {
    if (i < current && current - i === delta){
      range.push('...');
      range.splice(1, i - 2)
    } else if (i > current && i - current === delta){
      range.push('...');
      break;
    } else {
      range.push(i);
    }
  }
  range.push(last);

  return range;
}

/* 
Test it:

for (let i = 1, l = 20; i <= l; i++)
    console.log(`Selected page ${i}:`, pagination(i, l));

Expected output:

Selected page 1: [1, 2, 3, "...", 20]
Selected page 2: [1, 2, 3, 4, "...", 20]
Selected page 3: [1, 2, 3, 4, 5, "...", 20]
Selected page 4: [1, 2, 3, 4, 5, 6, "...", 20]
Selected page 5: [1, 2, 3, 4, 5, 6, 7, "...", 20]
Selected page 6: [1, "...", 4, 5, 6, 7, 8, "...", 20]
Selected page 7: [1, "...", 5, 6, 7, 8, 9, "...", 20]
Selected page 8: [1, "...", 6, 7, 8, 9, 10, "...", 20]
Selected page 9: [1, "...", 7, 8, 9, 10, 11, "...", 20]
Selected page 10: [1, "...", 8, 9, 10, 11, 12, "...", 20]
Selected page 11: [1, "...", 9, 10, 11, 12, 13, "...", 20]
Selected page 12: [1, "...", 10, 11, 12, 13, 14, "...", 20]
Selected page 13: [1, "...", 11, 12, 13, 14, 15, "...", 20]
Selected page 14: [1, "...", 12, 13, 14, 15, 16, "...", 20]
Selected page 15: [1, "...", 13, 14, 15, 16, 17, "...", 20]
Selected page 16: [1, "...", 14, 15, 16, 17, 18, 19, 20]
Selected page 17: [1, "...", 15, 16, 17, 18, 19, 20]
Selected page 18: [1, "...", 16, 17, 18, 19, 20]
Selected page 19: [1, "...", 17, 18, 19, 20]
Selected page 20: [1, "...", 18, 19, 20]
*/

Easier to read and loops one less time