JavaScriptの再考：Death for

for



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for JavaScript?



for



(. mutation of state — — . ) (. side effects — — . ), .



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, (. mutable state — — . ), , . , .



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const cats = [
 { name: 'Mojo',    months: 84 },
 { name: 'Mao-Mao', months: 34 },
 { name: 'Waffles', months: 4 },
 { name: 'Pickles', months: 6 }
]
var kittens = []
// ,     for
for (var i = 0; i < cats.length; i++) {
 if (cats[i].months < 7) {
   kittens.push(cats[i].name)
 }
}
console.log(kittens)

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, .



-, :

const isKitten = cat => cat.months < 7
var kittens = []
for (var i = 0; i < cats.length; i++) {
 if (isKitten(cats[i])) {
   kittens.push(cats[i].name)
 }
}

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

— . “ 7 ” “ ” — . . 7 ? . , !



, isKitten



, , .



— ( ) . , .

const isKitten = cat => cat.months < 7 
const getName = cat => cat.name
var kittens = []
for (var i = 0; i < cats.length; i++) {
 if (isKitten(cats[i])) {
   kittens.push(getName(cats[i]))
 }
}

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

filter



map



, , , (filter



map



— . ) . , .

const isKitten = cat => cat.months < 7
const getName = cat => cat.name
const kittens =
 cats.filter(isKitten)
     .map(getName)

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, kittens.push(...)



. var



.

const



var



let

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:

const isKitten = cat => cat.months < 7
const getName = cat => cat.name
const getKittenNames = cats =>
 cats.filter(isKitten)
     .map(getName)
const cats = [
 { name: 'Mojo',    months: 84 },
 { name: 'Mao-Mao', months: 34 },
 { name: 'Waffles', months: 4 },
 { name: 'Pickles', months: 6 }
]
const kittens = getKittenNames(cats)
console.log(kittens)

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

filter map . : .

• Functional JavaScript: Decoupling methods from their objects
• Functional JavaScript: Function Composition For Every Day Use.

break

, “ break



”, “ JavaScript: break GOTO ”.

• Rethinking JavaScript: Replace break by going functional

. for



?



, - (@joelnet), , .



!