boo.js

var numbers = [1, 2, 5, 6, 7, 9, 10];
var target = 6;

function takeWhile(arr, fn, cb) {
    var out = [];
    for (var i = 0; i < arr.length; i++) {
        if (fn(arr[i], i)) out.push(arr[i]);
        else break;
    }
    return out;
}

console.log(takeWhile(numbers.slice(numbers.indexOf(target) + 1), function(res, i) {
    return res == target + i + 1;
}).concat(takeWhile(numbers.slice(0, numbers.indexOf(target)).reverse(), function(res, i) {
    return res == target + i - 1;
})))