In certain situations, it may happen that we have undefined
or generally falsy values in Array structures. For instance when reading and filling data from some unknown sources like Databases or HTML structures. Like
var data = [42, 21, undefined, 50, 40, undefined, 9]
Since that might cause trouble when looping over such arrays and working on the elements, what is the best practice to remove undefined
(falsy values) ?
To use Array.prototype.filter
here might be obvious. So to remove only undefined values we could call
var data = [42, 21, undefined, 50, 40, undefined, 9];
data = data.filter(function( element ) {
return element !== undefined;
});
If we want to filter out all the falsy values (such as 0 or null) we can use return !!element;
instead.
But we can do it slighty more elegant, by just passing the Boolean
constructor function, respectively the Number
constructor function to .filter
:
data = data.filter( Number );
That would do the job in this instance, to generally remove any falsy value, we would call
data = data.filter( Boolean );
Since the Boolean()
constructor returns true
on truthy values and false
on any falsy value, this is a very neat option.