CODEWITHSUNDEEP
ecmascript-6
GoOlga
GoOlga

Reputation: 234

Return value from lambda expression

I have a trouble to understand the return value from line #14. My question is about: fn(acc), x in one line. How is it possible to write it in a block instead? Like: {return fn(acc), x} ?? Of course it wouldn't work. Does any one can write it down as a block code instead of a one-line code? 

1  const scream = str => str.toUpperCase()
2  const exclaim = str => `${str}!`
3  const repeat = str => `${str} ${str}`
4  
5  const string = 'Hello world'
6  
7  // Nested
8  // const result1= repeat(exclaim(scream(string)))
9  // console.log(result1)
10 // HELLO WORLD! HELLO WORLD!
11
12 // Instead of nesting, compose your functions into a new function
13 const compose = (...fns) => x =>
14    fns.reduceRight((acc, fn) => fn(acc), x)
15
16 const enhance = compose(repeat, exclaim, scream)
17 const result2 = enhance(string)
18 console.log(result2)
19 // HELLO WORLD! HELLO WORLD!

Thanks!

Upvotes: 1

Views: 58

Answers (1)

that other guy
that other guy

Reputation: 123540

The thing to note is mostly that reduceRight is a reverse for loop. Here is the same function with loops and regular function expressions:

const scream = str => str.toUpperCase()
const exclaim = str => `${str}!`
const repeat = str => `${str} ${str}`

const string = 'Hello world'

// (...fns) =>
function compose() {
  var fns = arguments;
  // x =>
  return function(x) {
    var acc = x;
    // fns.reduceRight((acc, fn) =>
    for(var i = fns.length-1; i>=0; i--) {
      var fn = fns[i];
      // fn(acc)
      acc = fn(acc);
    }
    return acc;
  }
}

const enhance = compose(repeat, exclaim, scream)
const result2 = enhance(string)
console.log(result2)

Upvotes: 1

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