why ?? is not working with ternary operator答案

【问题标题】：why ?? is not working with ternary operatorwhy ?? is not working with ternary operator
【发布时间】：2022-11-20 20:26:42
【问题描述】：

why Null Coalescing is not working with ternary operator. I would expect to get tdy.

const test = {
  todo: {
    day: 'tdy'
  }
}

const filterDayRange = [{
    day: 'mon'
}]

 const result =
      test.todo?.day ?? filterDayRange.length > 0 ? filterDayRange[0].day : 'tdy';

console.log(result)


// expected Output: tdy

Playground link

【问题讨论】：

标签： typescript

【解决方案1】：

I simply add Parantheses :

 test.todo?.day ?? (filterDayRange.length > 0 ? filterDayRange[0].day : 'tdy');

and now it works fine

【讨论】：

【解决方案2】：

Everythings seems to work as expected. filterDayRange.length > 0 evaluates to truth. You can test it by replacing the result expressions in ternary operator

const test  = {
  todo: { 
    day: 'tdy'
  }
}

const filterDayRange = [{
    day: 'mon'
}]

 const result =
      test.todo?.day ?? filterDayRange.length > 0 ? 'tdy': filterDayRange[0].day;

console.log(result)

【讨论】：

【解决方案3】：

separate the ternary operator will fix the issue

let result = test.todo?.day ?? (filterDayRange.length > 0 ? filterDayRange[0].day : 'tdy')

【讨论】：