4 个强大的 JavaScript 运算符

null ?? 5 // => 5
3 ?? 5 // => 3

var prevMoney = 1
var currMoney = 0
var noAccount = null
var futureMoney = -1
function moneyAmount(money) {
return money || `账户未开通`
}
console.log(moneyAmount(prevMoney)) // => 1
console.log(moneyAmount(currMoney)) // => 账户未开通
console.log(moneyAmount(noAccount)) // => 账户未开通
console.log(moneyAmount(futureMoney)) // => -1

var currMoney = 0
var noAccount = null
function moneyAmount(money) {
  return money ?? `账户未开通`
}
moneyAmount(currMoney) // => 0
moneyAmount(noAccount) // => `账户未开通`

var x = null
var y = 5
console.log(x ??= y) // => 5
console.log(x = (x ?? y)) // => 5

function gameSettingsWithNullish(options) {
  options.gameSpeed ??= 1
  options.gameDiff ??= 'easy' 
  return options
}
function gameSettingsWithDefaultParams(gameSpeed=1, gameDiff='easy') {
  return {gameSpeed, gameDiff}
}
gameSettingsWithNullish({gameSpeed: null, gameDiff: null}) // => {gameSpeed: 1, gameDiff: 'easy'}
gameSettingsWithDefaultParams(undefined, null) // => {gameSpeed: null, gameDiff: null}

var travelPlans = {
  destination: 'DC',
  monday: {
    location: 'National Mall',
    budget: 200
  }
}
console.log(travelPlans.tuesday?.location) // => undefined

function addPlansWhenUndefined(plans, location, budget) {
  if (plans.tuesday?.location == undefined) {
    var newPlans = {
      plans,
      tuesday: {
        location: location ?? "公园",
        budget: budget ?? 200
      },
    }
  } else {
    newPlans ??= plans; // 只有 newPlans 是 undefined 时，才覆盖
    console.log("已安排计划")
  }
  return newPlans
}
// 译者注，对象 travelPlans 的初始值，来自上面一个例子
var newPlans = addPlansWhenUndefined(travelPlans, "Ford 剧院", null)
console.log(newPlans)
// => { plans: 
// { destination: 'DC',
// monday: { location: '国家购物中心', budget: 200 } },
// tuesday: { location: 'Ford 剧院', budget: 200 } }
newPlans = addPlansWhenUndefined(newPlans, null, null)
// logs => 已安排计划
// returns => newPlans object

function checkCharge(charge) {
  return (charge > 0) ? '可用' : '需充值' 
}
console.log(checkCharge(20)) // => 可用
console.log(checkCharge(0)) // => 需充值

var budget = 0
var transportion = (budget > 0) ? '火车' : '步行' 
console.log(transportion) // => '步行'

var x = 6
var x = (x !== null || x !== undefined) ? x : 3
console.log(x) // => 6

function nullishAssignment(x,y) {
  return (x == null || x == undefined) ? y : x 
}
nullishAssignment(null, 8) // => 8
nullishAssignment(4, 8) // => 4

function addPlansWhenUndefined(plans, location, budget) {
 var newPlans =
   plans.tuesday?.location === undefined
     ? {
         plans,
         tuesday: {
           location: location ?? "公园", 
           budget: budget ?? 200
         },
       }
     : console.log("已安排计划");
 newPlans ??= plans;
 return newPlans;
}

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