JAVASCRIPT

javascript function required arguments

const isRequired = () => { throw new Error('param is required'); };

const hello = (name = isRequired()) => { console.log(`hello ${name}`) };

// This will throw an error because no name is provided
hello();

// This will also throw an error
hello(undefined);

// These are good!
hello(null);
hello('David');

javascript function parameters type required

/* @flow */
function foo(x: string, y: number): string {
  return x.length * y;
}
foo('Hello', 42);