Parameters are used in the defintion of functions and constructors.

Parameters are separated by comma. There are positional, optional and rest parameters.

Positional parameters

parametername [ ( : | like ) type ]    

Example:

function x(a, b : string) {}

The function has two parameters. The second parameter has a type annotation, which indicates that the function must be called with a value of the specified type. (Se like for explanation of the like-constraint).

Optional parameters

parametername [ ( : | like ) type ]  = expression  

An optional parameter is provided with a default value. If a value is not provided in the method call, the parameter gets the default value.

function x(c = 100) { return c; }
x(17); // returns 17
x(); // returns 100

Rest parameter

... parametername 

The rest parameter becomes an array of all arguments in excess of the ones that matches other parameters. Example:

function x(...d) {
    return d.length;
}
x(1,2,3); // returns 3
x(); // returns 0

A rest parameter must always be the last parameter in the parameter list.