Replace a value if null or undefined in JavaScript

Question

Hello, I have a requiremnt to apply the ?? C# operator to JavaScript world and don't know how. Consider this in C#:

int i?=null;
int j=i ?? 10;//j is now 10

Now I have this set up in JavaScript:

var options={
       filters:{
          firstName:'abc'
       } 
    };
var filter=options.filters[0]||'';//should get 'abc' here, it doesn't happen
var filter2=options.filters[1]||'';//should get empty string here, because there is only one filter

How do I do it correctly?

Thanks.

EDIT: I spotted half of the problem: I can't use the 'indexer' notation to objects (my_object[0]). Is there a way to bypass it? (I don't know the names of the filters properties beforehand and don't want to itereate over them).

Answer 1

Here’s the JavaScript equivalent:

var i = null;
var j = i || 10; //j is now 10

Note that the logical operator || does not return a boolean value but the first value that can be converted to true.

Additionally use an array ob objects instead of one single object:

var options = {
    filters: [
        {
            name: 'firstName',
            value: 'abc'
        }
    ]
};
var filter  = options.filters[0] || '';  // is {name:'firstName', value:'abc'}
var filter2 = options.filters[1] || '';  // is ''

That can be accessed by index.

Answer 2

I spotted half of the problem: I can't use the 'indexer' notation to objects (my_object[0]). Is there a way to bypass it?

No; an object literal, as the name implies, is an object, and not an array, so you cannot simply retrieve a property based on an index, since there is no specific order of their properties. The only way to retrieve their values is by using the specific name:

var someVar = options.filters.firstName; //Returns 'abc'

Or by iterating over them using the for ... in loop:

for(var p in options.filters) {
    var someVar = options.filters[p]; //Returns the property being iterated
}