Question

For example, if I have these arrays:

var name = ["Bob","Tom","Larry"];
var age =  ["10", "20", "30"];

And I use name.sort() the order of the “name” array becomes:

var name = ["Bob","Larry","Tom"];

But, how can I sort the “name” array and have the “age” array keep the same order? Like this:

var name = ["Bob","Larry","Tom"];
var age =  ["10", "30", "20"];

Answer 1

You can sort the existing arrays, or reorganize the data.

Method 1:
To use the existing arrays, you can combine, sort, and separate them:
(Assuming equal length arrays)

var names = ["Bob","Tom","Larry"];
var ages =  ["10", "20", "30"];

//1) combine the arrays:
var list = [];
for (var j = 0; j < names.length; j++) 
    list.push({'name': names[j], 'age': ages[j]});

//2) sort:
list.sort(function(a, b) {
    return ((a.name < b.name) ? -1 : ((a.name == b.name) ? 0 : 1));
    //Sort could be modified to, for example, sort on the age 
    // if the name is the same. See Bonus section below
});

//3) separate them back out:
for (var k = 0; k < list.length; k++) {
    names[k] = list[k].name;
    ages[k] = list[k].age;
}

This has the advantage of not relying on string parsing techniques, and could be used on any number of arrays that need to be sorted together.

Method 2: Or you can reorganize the data a bit, and just sort a collection of objects:

var list = [
    {name: "Bob", age: 10}, 
    {name: "Tom", age: 20},
    {name: "Larry", age: 30}
    ];

list.sort(function(a, b) {
    return ((a.name < b.name) ? -1 : ((a.name == b.name) ? 0 : 1));
});

for (var i = 0; i<list.length; i++) {
    alert(list[i].name + ", " + list[i].age);
}
​

For the comparisons,-1 means lower index, 0 means equal, and 1 means higher index. And it is worth noting that sort() actually changes the underlying array.

Also worth noting, method 2 is more efficient as you do not have to loop through the entire list twice in addition to the sort.

http://jsfiddle.net/ghBn7/38/

Bonus Here is a generic sort method that takes one or more property names.

function sort_by_property(list, property_name_list) {
  list.sort((a, b) => {
    for (var p = 0; p < property_name_list.length; p++) {
      prop = property_name_list[p];
      if (a[prop] < b[prop]) {
        return -1;
      } else if (a[prop] !== a[prop]) {
        return 1;
      }
    }
    return 0;
  });
}

Usage:

var list = [
        {name: "Bob", age: 10}, 
        {name: "Tom", age: 20},
        {name: "Larry", age: 30},
        {name: "Larry", age: 25}
    ];

sort_by_property(list, ["name", "age"]);

for (var i = 0; i<list.length; i++) {
    console.log(list[i].name + ", " + list[i].age);
}

Output:

• Bob, 10
• Larry, 25
• Larry, 30
• Tom, 20