Sometimes you may want to manipulate date or date/time fields. For example, you may want to assure that a start time is before an end time on a form. Or perhaps you want to default a date to 10 days from now. This article will go over these two examples as a way of explaining the method recommended to do such things.
We will be working with this simple test item:
For the first example, we will review setting a default date of 10 days from now into the start date. The steps for this are:
- In the builder, select the page of the question you wish to default. It will have an events section (currently empty/collapsed).
- Click on the Events section to open it, then click on “Add Event”
- Fill out the details of the event to set the desired field.
Type: Pages have two kinds of events: Load and Submit. In this case, we want Load because we want this to run when the page comes up, not when the person submits it.
Name: You can name the event whatever you wish.
Run-If Condition: The event will only run if this condition evaluates to true. In this case, we only want to set the default into the field if it is empty/null. If someone has already filled it in (and perhaps saved the event and is coming back to it), we wouldn’t want to run the event.
Bridged Resource: This is used only if you are using bridge data for your event, and in this case we are not, so we say “None”.
Code: Because we specified “Custom” in action, we get a code block to specify our code within. The code within this block in this case is:
K('field[Start Date]').value(moment().add(10, 'days').format('YYYY-MM-DD'));
This is equivalent to:
//get current date as a moment var currentMoment = moment(); //calculate 10 days from now var desiredMoment = currentMoment.add(10, 'days'); //format desired moment var formattedMoment = desiredMoment.format('YYYY-MM-DD'); //set start date field K('field[Start Date]').value(formattedMoment);
But as specified here Moment.js supports method chaining, so the lengthy format can be collapsed for brevity.
For the second example, we will make sure that the Start Date is before the End Date. This will also use the Moment.js library. The steps are:
- Click on the field you want to add validation to, Start Date in this case, so that it’s options appear on the right (including validation).
- The next step is to click Enabled for the Custom Constraint. This will expose the two fields that control the action–the Expression (to be evaluated) and the Message to be displayed if the test fails.
In this case, the expression is:
values('End Date') != null && moment(values('Start Date')).isBefore(moment(values('End Date')))
This says that the End Date must have a value, and that the moment represented by the start date is before the moment represented by the end date. In this case, we cannot assign variables and expand it out because we only have one line to work with. To fill in the values from the form, kapp, and space, the variables menu attached to the expression field can be used.
Once the constraint is in place and saved, the results would look like this when submission is attempted that does not meet the constraint: