Build a set of if-elseif-else switches using functions

conditional.js

const conditional = () => {
  let elseThen = i => i;
  const conditions = [];
  function cond (val) {
    const res = conditions
      .find(condPair => condPair.test(val));
    
    return res
      ? res.then(val)
      : elseThen(val);
  }
  cond.ifThen = (test, then) => {
    conditions.push({ test, then });
    return cond;
  }
  cond.elseThen = (then) => {
    elseThen = then;
    return cond;
  }
  return cond;
}


const myTest = conditional()
  .ifThen(val => val % 2 === 1, val => `${val} is odd`)
  .ifThen(val => val % 2 === 0, val => `${val} is even`)
  .ifThen(val => isNaN(val), val => `${val} is not a number`)
  .elseThen(val => `${val} is completly unknown to me`);

console.log(myTest(1));
console.log(myTest(2));
console.log(myTest(55));
console.log(myTest(16554));
console.log(myTest('123s'));
console.log(myTest(1/0));