Mastering TypeScript 3 - Third Edition

Optional tuple elements

Similar to function signatures, we can also have optional tuple elements. This is achieved by using the ? symbol within a tuple definition, as follows:

let optionalTuple: [string, boolean?];optionalTuple = ["test2", true];console.log(`optionalTuple : ${optionalTuple}`);optionalTuple = ["test"];console.log(`optionalTuple : ${optionalTuple}`);

Here, we have a defined variable named optionalTuple that has a mandatory string property, and an optional boolean property. We then assign a value of ["test2", true] to it, and log it to the console. We are then assigning a value of ["test"] to the same tuple, and log the value to the console. As the second property of the optionalTuple is, in fact, optional, this code will compile ...