Javascript - Numeric associative array alternatives

Just use an object literal instead of an array:

var extensions = {
    28: […]
};

You can access it by extensions[28] (or extensions["28"]).

You have two main options:

Use an Object

var extensions = {
    28:[
        {
            name:"watch errors",
            command: "tail -f error.log"
        },
        {
            name:"clear errors",
            command: "> error.log"
        }
    ] };
console.log(extensions[28][0].name); // "watch errors"

Note that you can't use extensions.28 to access this, you need to use extensions[28].

Use a Sparse Array

The array you're looking for here is perfectly legal...you just can't specify it as a literal.

var extensions = [];
extensions[28] = [
            {
                name:"watch errors",
                command: "tail -f error.log"
            },
            {
                name:"clear errors",
                command: "> error.log"
            }
        ];

console.log(extensions[28][0].name); // "watch errors"

Now you have an array, with a value at index 28, and indices 0-27 undefined.

Now, it's worth noting as a caveat here that lots of people hate sparse arrays in javascript. Also, you'll need to be careful iterating through them, accessing length, etc. But they ARE a valid part of the language, and this is one use-case for them.

This should work if you use object notation. I would also recommend enclosing the 28 in quotes. This will help avoid potential confusion of thinking it is an array index when it is not.

var objects = [
    {id:15,name:"client John Doe"},
    {id:28,name:"server"}
]

var extensions = {
    "28":[
        {
            name:"watch errors",
            command: "tail -f error.log"
        },
        {
            name:"clear errors",
            command: "> error.log"
        }
    ]
}

You could then read the property as extensions["28"][0], you can't do extensions.28[0] however.