More of an exercise in 'what-if', I was wondering if the following was possible:

output = convert(1200).from('mm').to('inches')

where 'from' and 'to' are functions (or properties) of 'convert' as opposed to the more standard:

    output = convert(1200, 'mm', 'inches')

or:

    output = convert(value = 1200, from = 'mm', to = 'inches')

addendum: I'm guessing the closest would be:

output = convert({ value: 1200, from: 'mm', to: 'inches' });
 
function convert({ value, from, to } = {}){
  // ...do stuff here...
}

CodePudding user response：

Yes, it's possible. Example:

function convert(val) {
  const units = {
    mm: 1,
    cm: 10,
    dm: 100,
    m: 1000,
    in: 25.4,
    inches: 25.4,
    inch: 25.4,
    ft: 304.8,
    feet: 304.8,
    foot: 304.8,
    yd: 914.4,
    yard: 914.4,
    yards: 914.4
  }
  return {
    from(unit1) {
      return {
        to(unit2) {
          return val * units[unit1] / units[unit2];
        }
      };
    }
  };
}

const output = convert(1200).from('mm').to('inches');

console.log(output);

console.log(convert(47.24409448818898).from('inches').to('mm'));
console.log(convert(123).from('m').to('yards'));

convert returns an object with a from method. from returns an object with a to method. to returns a number. The temporary values are stored in a closure.

CodePudding user response：

Treating this as a syntax rather than a design question, here is an ugly but working solution.

However, I would like to encourage you to refactor it or reconsider whether this functional API is necessary.

const convert = (num) => ({
  from: (inputUnit) => {
    switch (inputUnit) {
      case "mm":
        return {
          to: (outputUnit) => {
            switch (outputUnit) {
              case "inches":
                return num / 25.4;
            }
          },
        };
    }
  },
});

console.log(
  convert(1200).from("mm").to("inches")
)

CodePudding user response：

[Updated answer considering the comment from Teemu]

Create an object constructor with the convert, from and to functions, and properties to store the values passed to each corresponding function when called. In both convert and from functions, return the instance via 'return this' and return the answer in the to function.

https://www.w3schools.com/JS/js_object_constructors.asp

function Converter() {
  this.value = 0;
  this.fromUnit = '';
  this.toUnit = '';
  this.convert = function(value) {
   ... 
   return this
  } 
 this.from = function(unit) {... return this} 
 this.to = function(unit) {... return answer} 
}

const converter = new Converter()
converter.convert(...).from(...).to(...)

You can also follow the Class syntax on ES6 JavaScript. https://www.w3schools.com/Js/js_classes.asp

Pardon the formating as I'm answering on my phone.