Similar to the Empty function, this function provides a conditional evaluation of an expression. If the expression evaluates as null, the function will output true, otherwise it will output false.



Ordinal Type Required Description
1 String True A variable or nested function to evaluate

NOTE: This function only evaluates Data Extension field values. When used to evaluate other contexts, it will output false.


In the following example, a form is displayed on a personalized landing page and the code conditionally displays a field.


var @phone
set @phone = Lookup("Members", "Phone", "Subscriber Key", _subscriberKey)

if IsNull(@phone) then


<label>Phone</label> <input type="text" name="phone">

%%[ endif ]%%


If the Data Extension Phone field does not contain a value for a Subscriber, the IsNull function will evaluate to true and an input field will be displayed on the form.

<label>Phone</label> <input type="text" name="phone">