Undefined startup parameter if its name contains a hyphen, e.g. "sap-system"

A general Fiori launchpad tile is set up with a parameter 'sap-system=SystemAlias'.

Logging this.getComponentData().startupParameters returns:

{sap-system: Array(1)}

I've faced the issue to access the parameter by calling

let sSystem = this.getComponentData().startupParameters.sap-system[0];

The w3schools in Naming Conventions says that

Hyphens are not allowed in JavaScript names.

Is there a way to access such parameters with a hyphen, e.g. "sap-system"?