How to Merge sorted Arrays in JavaScript

The native implementations are not always the fastest (as you may have noticed) and have, historically, been somewhat sluggish, due to extensive error checking. That being said, there may be performance enhancements in the future, due to more robust integration with the hardware or routines specifically built to optimize certain tasks. If you write your own code, your application won't be able to take advantage of these boosts in performance once they're implemented. It's up to you to decide where the advantages lie and what the risks are.

At any rate, I've written a prettier version of your optimized code for funsies:

function mergeSorted(a,b){
    var alen = a.length
      , blen = b.length
      , i, j, k = j = i = 0
      , answer = new Array(alen + blen)
    ;//var

    while(i < alen && j < blen)
                    answer[k++] = a[i].name < b[j].name ? a[i++] : b[j++];
    while(i < alen) answer[k++] = a[i++];
    while(j < blen) answer[k++] = b[j++];

    return answer;
}

Update:

Seeing as it is current_year this would now be:

const mergeAll = (...arrays) => arrays.reduce(mergeSorted);

Original:

If you're feeling functional this is a perfect place to use reduce.

var mergeAll = function(){
    return Array.prototype.slice.call(arguments).reduce(mergeSorted);
};

example:

var a = [{name:"a"}, {name:"b"}, {name:"m"}, {name:"x"}];
var b = [{name:"a"}, {name:"e"}, {name:"i"}, {name:"o"}];
var c = [{name:"g"}, {name:"h"}, {name:"m"}, {name:"n"}];

console.log(mergeAll(a,b,c).map(function(x){return x.name;}));

jsfiddle: http://jsfiddle.net/FeT6m/

The standard and most understanding code I believe..

function mergeArray(arr1, arr2) {
 var new_array = [];
 var i = 0,
     j = 0,
     index = 0;

 while (new_array.length != (arr1.length + arr2.length) - 1) {
     if (arr1[i] < arr2[j]) {
         new_array.push(arr1[i]);
         i++;
     } else {
         new_array.push(arr2[j]);
         j++;
     }
 }
 return new_array;
}

Function call:

var merged_array = mergeArray([1,6,9,95], [2,7,10,11,14,18]);