4个你傻傻分不清楚的关于 ？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 || `You currently do not own an account in the bank`
}
console.log(moneyAmount(prevMoney)) // => 1
console.log(moneyAmount(currMoney)) // => `You currently do not own an account in the bank`
console.log(moneyAmount(noAccount)) // => `You currently do not own an account in the bank`
console.log(moneyAmount(futureMoney))//  => -1

var currMoney = 0
var noAccount = null
function moneyAmount(money) {
  return money ?? `You currently do not own an account in the bank`
}
 moneyAmount(currMoney) // => 0
 moneyAmount(noAccount) // => `You currently do not own an account in the bank`

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(null, null) // => { gameSpeed: null, gameDiff: null }

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

function addPlansWhenUndefined(plans, location, budget) {
  if (plans.tuesday?.location === undefined) {
    var newPlans = {
      plans,
      tuesday: { location: location ?? "Park", budget: budget ?? 200 },
    };
  } else {
    newPlans ??= plans; //will only override if newPlans is undefined
    console.log("Plans have already been added!");
  }
  return newPlans;
}
var newPlans = addPlansWhenUndefined(travelPlans, "Ford Theatre", null);
console.log(newPlans) // => { plans:
                  //{ destination: 'DC',
                  // monday: { location: 'National Mall', budget: 200 } },
                  // tuesday: { location: 'Ford Theatre', budget: 200 } }
newPlans = addPlansWhenUndefined(newPlans, null, null) // logs => Plans have already been added!
                                                      // returns => newPlans object

function checkCharge(charge) {
return (charge > 0) ? 'Ready for use' : 'Needs to charge'
}
console.log(checkCharge(20)) // => 'Ready for use'
console.log(checkCharge(0)) // => 'Needs to charge'

var budget = 0
var transportion = (budget > 0) ? 'Train' : 'Walking'
console.log(transportion) // => 'Walking'

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
}
var x = nullishAssignment(null, 8) // => 8
var y = nullishAssignment(4,8) // => 4

function addPlansWhenUndefined(plans, location, budget) {
  var newPlans =
    plans.tuesday?.location === undefined
      ? {
          ...plans,
          tuesday: { location: location ?? "Park", budget: budget ?? 200 },
        }
      : console.log("Plans have already been added!");
  newPlans ??= plans;
  return newPlans;
}