JavaScript 特性技巧5大实用技巧

• const composeM = chainMethod => (...ms) => ( ms.reduce((f, g) => x => g(x)[chainMethod](f)) ); const composePromises = composeM('then'); const label = 'API call composition';

  // a => Promise(b)  const getUserById = id => id === 3 ?    Promise.resolve({ name: 'Kurt', role: 'Author' }) : undefined;
  // b => Promise(c)  const hasPermission = ({ role }) => (    Promise.resolve(role === 'Author')  );
  // Compose the functions (this works!)  const authUser = composePromises(hasPermission, getUserById);  authUser(3).then(trace(label)); // true

• function evenSum(numbers) { let result = 0;

    for (let i = 0; i < numbers.length; i++) {        let number = numbers[i]        if (number % 2 === 0) {            result += number;        }    }
    return result;}

const evenSum = numbers => numbers    .filter(i => i % 2 === 0)    .reduce((a, b) => a + b)

• const cache = require('memory-cache');

function getDataFromCache(key) {  const cachedData = cache.get(key);  if (cachedData) {    return cachedData;  }
  // If data is not in cache, fetch it from the source  const data = fetchDataFromSource();
  // Store data in cache for future use  cache.put(key, data, 60000); // Cache for 60 seconds
  return data;}

// Import stylesheetsimport './style.css';
// Write JavaScript code!const appDiv = document.getElementById('app');appDiv.innerHTML = `<h1>Open the console to see results</h1>`;
class Person {  //_name = "Nee";  //_name = ["Nee", "Ra"];  _name = { first: "Nee", middle: "L" };
  get name() {    return this._name;  }
  set name(value) {    console.log('In setter', value);    this._name = value;  }}
let p = new Person();//p.name = "Ra";                        // Setter executes//p.name.push("Lee");                   // Setter doesn't execute//p.name = [...p.name, "Lee"];          // Setter executes//p.name.middle = "Lee";                // Setter doesn't executep.name = { ...p.name, middle: "Lee" };  // Setter executes

match = function () {  var unify = unification.unify;
  function match_aux(patterns, value) {    var i, result;
    for (i = 0; i < patterns.length; i += 1) {      result = unify(patterns[i][0], value);      if (result) {        return patterns[i][1](result);      }    }    return undefined;  }
  return function(patterns, value) {    return match_aux(patterns, value);  };}();
var fact = function (n) {  return match([    [0, function() { return 1; }],    [$('n'), function(result) {      return result.n * fact(result.n - 1);     }]  ], n);};