How can I set the default sort order on the primeng datatable?

I figured it out. These two attributes should be added:

sortField="userName" [sortOrder]="-1"

The sortField matches the column name and the sortOrder can be either 1 for ascending and -1 for descending.

Here’s the working solution:

<p-dataTable [value]="webUserSummaryList" [rows]="10"  reorderableColumns="true" sortField="userName" sortOrder="-1">
<p-column field="userName" header="Username" [filter]="true" [sortable]="true"></p-column>
<p-column field="emailAddress" header="Email" [filter]="true" [sortable]="true"></p-column>
<p-column field="firstName" header="First Name" [filter]="true" [sortable]="true"></p-column>
<p-column field="lastName" header="Last Name" [filter]="true" filterMatchMode="contains" [sortable]="true"></p-column>