Better (Functional) alternate to multiple switch cases in JS-CodePudding

The Object Lookup method is very popular in JS and used as a better replacement for Switch-case statements e.g.

function phoneticLookup(val) {
  var result = "";

  switch(val) {
    case "alpha":
      result = "Adams";
      break;
    case "bravo":
      result = "Boston";
      break;
    case "charlie":
      result = "Chicago";
      break;
  }
  return result;
}


function phoneticLookup(val) {
  var result = "";

  var lookup = {
    "alpha": "Adams",
    "bravo": "Boston",
    "charlie": "Chicago",
  };

  result = lookup[val];
  return result;
}

But if the switch case is like the one below, as you can see multiple cases return the same result. How can we write it in a better way using objects, map, or any other way (not using if-else) in JS?

let continent = '';
switch (country) {
   case "China":
   case "India":
   case "Nepal": 
       continent = 'Asia';
       break;
   case "UK":
   case "France":
   case "Poland": 
       continent = 'Europe';
       break;
   case "Egypt":
   case "Zimbave":
   case "Somalia": 
       continent = 'Africa';
       break;
   default: 
       continent = 'Other'
       break;
}

CodePudding user response：

You have a few options. The pattern matching propsal is Stage 1 and may never make it into the standard. You could write a custom switch/match function as in this answer. For this specific case you actually could use an object lookup, just a little differently:

const continents = {
  "Africa": ["Egypt", "Ghana"], // etc
  "Asia": ["China", "Bhutan"], // etc
}

const assignContinent = (country) => {
  const possibleMatch = Object.entries(continents)
    .find((continent) => continent[1].includes(country))
  return possibleMatch ? possibleMatch[0] : "Other"
}

CodePudding user response：

For performance I recommend defining a mapping with repetition of continent:

countryToContinentMap = {
   China:   'Asia',
   India:   'Asia',
   Nepal:   'Asia',
   UK:      'Europe',
   France:  'Europe',
   Poland:  'Europe',
   Egypt:   'Africa',
   Zimbave: 'Africa',
   Somalia: 'Africa'
}

function getContinent(country) {
    return countryToContinentMap[country] || 'Other';
}

console.log('Nepal => '   getContinent('Nepal'));
console.log('Xomur => '   getContinent('Xomur'));

Output:

Nepal => Asia
Xomur => Other

To make it easier o define the mapping, you could do it as @Zac Anger did, then programmatically reverse the mapping once before use.