A Dead Simple Intro to Arrow Function

emilyscone·2020년 12월 28일
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An arrow function expression is a compact alternative to a traditional function expression, but is limited and can't be used in all situations.

ES5 vs ES6

Basic Syntax with Multiple Parameters

// ES5
var multiplyES5 = function(x, y) {
  return x * y;
};
const multiplyES6 = (x, y) => x * y;

Basic Syntax with One Parameter

//ES5
var phraseSplitterEs5 = function phraseSplitter(phrase) {
  return phrase.split(' ');
};
//ES6
const phraseSplitterEs6 = phrase => phrase.split(" ");

console.log(phraseSplitterEs6("ES6 Awesomeness"));  // ["ES6", "Awesomeness"]
let double = n => n * 2;
// roughly the same as: let double = function(n) { return n * 2 }

alert( double(3) ); // 6

No Parameters

//ES5
var docLogEs5 = function docLog() {
    console.log(document);
};
//ES6
var docLogEs6 = () => { console.log(document); };
docLogEs6(); // #document... <html> ....

Object Literal Syntax

Return an object literal expression.

//ES5
var setNameIdsEs5 = function setNameIds(id, name) {
  return {
    id: id,
    name: name
  };
};
// ES6
var setNameIdsEs6 = (id, name) => ({ id: id, name: name });

console.log(setNameIdsEs6 (4, "Kyle"));   // Object {id: 4, name: "Kyle"}

Use Cases for Arrow Functions

const smartPhones = [
  { name:'iphone', price:649 },
  { name:'Galaxy S6', price:576 },
  { name:'Galaxy Note 5', price:489 }
];
// ES5
var prices = smartPhones.map(function(smartPhone) {
  return smartPhone.price;
});

console.log(prices); // [649, 576, 489]
// ES6
const prices = smartPhones.map(smartPhone => smartPhone.price);
console.log(prices); // [649, 576, 489]

Another example using filter method

const array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15];

// ES5
var divisibleByThrreeES5 = array.filter(function (v){
  return v % 3 === 0;
});

// ES6
const divisibleByThrreeES6 = array.filter(v => v % 3 === 0);

console.log(divisibleByThrreeES6); // [3, 6, 9, 12, 15]
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