ES6 learning path (IV) operator extension

Exponential operators

    const a = 3 ** 3
    console.log(a) // 27

The exponential operator evaluates from right to left

  const a = 1 ** 3 ** 2
    console.log(a) // 1
 First calculate 3 Of 2 The power is 9, Count again 1 Of 9 The power is 1
    const a = 2 ** 1 ** 2
    console.log(a) // 2
//  First calculate 1 Of 2 The power is 1 Count again 2 Of 1 Is 2

Chain judgment operator

    const obj = {
    
    }
    console.log(obj?.a) // undefined
    const obj1 = {
    
      a: 1
    }
    console.log(obj1?.a) // 1

obj?.a It can be understood as obj && obj.a || undefined

obj Is there any a This attribute , If you have any, take a value , If not, take undefined

More chain operations

    const obj = {
    
      a: {
    
        b: {
    
          c: 1
        }
      }
    }
    const d = obj && obj.a && obj.a.b && obj.a.b.c || undefined
    console.log(d) // 1

//  Chain operation 
    const obj = {
    
      a: {
    
        b: {
    
          c: 1
        }
      }
    }
    const d = obj?.a?.b?.c
    console.log(d) // 1

Operation function

    const obj = {
    
      a: {
    
        b: {
    
          c: () => {
    
            return 3
          }
        }
      }
    }
    const d = obj?.a?.b?.c()
    console.log(d) // 3

Short circuit mechanism

//  Chain operation 
    const obj = {
    
      a: {
    
        b: {
    
        }
      }
    }
    const d = obj?.a?.b?.c
    console.log(d) // undefined
    //  As long as there is one place where the value is undefined perhaps null, The program won't go back ( Judge ) 了 

NULL Judgment operator

The classic method of setting default values

    const foo = 1
    const bar = foo || 100
    console.log(bar)  // 1

If the programmer wants to foo by undefined perhaps null The default value is given when 100, So there's a problem . because foo by false perhaps 0 Or an empty string , Default values will also be given .

If you just want foo by undefined perhaps null Set default value when , You can do this

    const foo = ''
    const bar = foo ?? undefined
    console.log(bar) // ''

Other items will be added when they come across …