In typescript I have this object of type "Eular" (from three.js library). The object has 3 properties I can access x, y, z, like this

obj.z = 1;

But suppose I have this now

var key = "z";

How can I access the z property from using the variable key?

This doesn't work

obj[key] = 1;

I get this

Element implicitly has an 'any' type because expression of type 'string' can't be used to index type 'Euler'.
  No index signature with a parameter of type 'string' was found on type 'Euler'.ts(7053)

Thanks