@spa-tools/utilities

tern()

The native conditional ternary operator ? is awesome, but have you ever needed to execute a separate logic path for null/undefined values versus actual boolean values?

This is what the tern<T, F, U>() function is for. It's a simple utility that allows you to pass in a condition with three separate execution paths for true, false, and null/undefined.

• The generic T type is used to define the value type returned when true.
• The generic F type is used to define the value type returned when false.
• The generic U type is used to define the value type returned when null or undefined.

Usage

import { tern } from '@spa-tools/utilities';

// contrived function to get a random
// vote of either true, false, or null
function getRandomVote(): boolean | null {
  const randomNum = Math.random();
  if (randomNum < 0.33) {
    return true;
  } else if (randomNum < 0.66) {
    return false;
  } else {
    return null;
  }
}

const vote = getRandomVote();

console.log(
  'And the vote is:',
  // here the tern function decides which path to take
  // with the three possible branches based on vote value
  tern(vote, 'Yea!', 'Nay!', 'Abstained')
);

Arguments

Name	Type	Description
value	boolean | null | undefined	The expression/value to evaluate
whenTrue	T	The value to return when the expression evaluates to true
whenFalse	F	The value to return when the expression evaluates to false
whenNull	U	The value to return when the expression evaluates to null or undefined

Returns

Returns either T, F, U, accordingly.