Question

I have JSON objects that have several properties such as an id and name. I store them in a JavaScript array and then based on a dropdownlist I want to retrieve the object from the JavaScript array based on its id.

Suppose an object has id and name, how do I select them from my array variable?

var ObjectsList = data;
var id = $("#DropDownList > option:selected").attr("value");
ObjectsList["id=" + id];

Answer 1

Since you already have jQuery, you could use $.grep:

Finds the elements of an array which satisfy a filter function. The original array is not affected.

So something like this:

var matches = $.grep(ObjectsList, function(e) { return e.id == id });

that will leave you with an array of matching entries from ObjectsList in the array matches. The above assumes that ObjectsList has a structure like this:

[
    { id: ... },
    { id: ... },
    ...
]

If you know that there is only one match or if you only want the first then you could do it this way:

for(var i = 0, m = null; i < ObjectsList.length; ++i) {
    if(ObjectsList[i].id != wanted_id)
        continue;
    m = a[i];
    break;
}
// m is now either null or the one you want

There are a lot of variations on the for loop approach and a lot of people will wag a finger at me because they think continue is a bad word; if you don’t like continue then you could do it this way:

for(var i = 0, m = null; i < ObjectsList.length; ++i) {
    if(ObjectsList[i].id == wanted_id) {
        m = ObjectsList[i];
        break;
    }
}