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LT_2021_5_7

 LT_2021_5_7

baochanh18

May 07, 2021
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  1. Null演算子 OR演算子 let a = '' let b = 0

    let c = null let val = a || 'not found' // val = 'not found' val = b || 'not found' // val = 'not found' val = c || 'not found' // val = 'not found' Null演算子 let a = '' let b = 0 let c = null let val = a ?? 'not found' // val = '' val = b ?? 'not found' // val = 0 val = c ?? 'not found' // val = 'not found'
  2. Optional chaining let usersList = { user1: { name: 'a',

    age: 18}, User2: { name: 'b’, age: 20} }
  3. Optional chaining let usersList = { user1: { name: 'a',

    age: 18}, User2: { name: 'b’, age: 20} } let userName = usersList.user1.name //userName = a
  4. Optional chaining let usersList = { //user1: { name: 'a',

    age: 18}, User2: { name: 'b’, age: 20} } let userName = usersList.user1.name Error: Cannot read property 'name' of undefined
  5. Optional chaining let usersList = { //user1: { name: 'a',

    age: 18}, User2: { name: 'b’, age: 20} } let userName = usersList.user1 && usersList.user1.name //userName = undefined
  6. Optional chaining let usersList = { //user1: { name: 'a',

    age: 18}, User2: { name: 'b’, age: 20} } let userName = usersList.user1?.name //userName = undefined
  7. Optional chaining let usersList = { //user1: { name: 'a',

    age: 18}, User2: { name: 'b’, age: 20} } let userName = usersList.user1?.name //等価 //let temp = usersList.user1 //let username = ((temp === null || temp === undefined) ? Undefined : temp.name)