[brundolf]

Another short utility I often add (that I wish were a language feature):

  function given<T, R>(
    val: T|null|undefined,
    fn: (val: T) => R
  ): R|null|undefined {
    if (val != null) {
      return fn(val)
    } else {
      return val // null|undefined
    }
  }

  function greet(name: string|null) {
    return given(name, name =>  'Hello ' + name)
  }

This is equivalent to eg. Rust's .map()

Can also do a version without the null check for just declaring intermediate values:

  function having<T, R>(
    val: T,
    fn: (val: T) => R
  ): R {
    return fn(val)
  }

  const x = 
    having(2 * 2, prod =>
      prod + 1)