Unit Converter

Goals

• Write pure functions that map one value to another
• Use a lookup object to dispatch by string key
• Practice inverse conversions (round-trip)
• Organize related functions into one module

Prerequisites

• Functions and return values
• Objects / dictionaries as lookup tables
• Basic arithmetic and unit awareness

Steps

2. 1

   Write the length conversions

   Define kmToMiles(km) and milesToKm(mi). The factor is 1 km ≈ 0.621371 miles. Keeping each conversion in its own function makes them easy to test and reuse.

   CodeCopy

   function kmToMiles(km) {
     return km * 0.621371;
   }
   function milesToKm(mi) {
     return mi / 0.621371;
   }

   Expected result

   kmToMiles(10) returns about 6.21371; milesToKm(6.21371) returns about 10.

4. 2

   Write the temperature conversions

   Define celsiusToFahrenheit(c) and fahrenheitToCelsius(f). The formulas are F = C*9/5 + 32 and C = (F - 32) * 5/9.

   CodeCopy

   function celsiusToFahrenheit(c) {
     return c * 9 / 5 + 32;
   }
   function fahrenheitToCelsius(f) {
     return (f - 32) * 5 / 9;
   }

   Expected result

   celsiusToFahrenheit(0) returns 32; fahrenheitToCelsius(98.6) returns about 37.

6. 3

   Build a dispatcher

   Create an object converters whose keys are conversion names and whose values are the functions. A convert(name, value) helper looks up the function and calls it. This pattern scales to many conversions without a giant if/else.

   CodeCopy

   const converters = {
     "km-to-miles": kmToMiles,
     "miles-to-km": milesToKm,
     "c-to-f": celsiusToFahrenheit,
     "f-to-c": fahrenheitToCelsius,
   };
   
   function convert(name, value) {
     const fn = converters[name];
     if (!fn) return "Unknown conversion";
     return fn(value);
   }

   Expected result

   convert("km-to-miles", 10) returns 6.21371; convert("c-to-f", 100) returns 212.

8. 4

   Verify round-trips

   A good conversion is invertible: converting back should return the original value (within rounding). Test one length and one temperature round-trip.

   CodeCopy

   console.log(milesToKm(kmToMiles(42)));       // ≈ 42
   console.log(fahrenheitToCelsius(celsiusToFahrenheit(25))); // ≈ 25

   Expected result

   Both lines print a number very close to 42 and 25 respectively.

   Show hint

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