You can define you own types using interfaces Thing describes and object literal with an a number property and a b string property. Even though the process function dosen't return a type We have given the compiler enogh information to infer that n at the bottom will be of type number.

gistfile1.ts

// 
interface Thing {
	a: number;
	b: string;
	c: boolean;
}


function process(x: Thing){
	return x.a;
}


var n = process({a: 10, b:'Beeby'});
n.toFixed(0.0);