1. Null-value merge operator:??

    If the left-hand operand is null or undefined, return the right-hand operand; otherwise, return the left-hand operand.

    null ?? 'huli' // huli
undefined ?? 'huli'  // huli
' ' ?? 'huli' / /"[]????'huli' / / []({})??'huli'  / / {}
NaN ?? 'huli' // NaN
false ?? 'huli' // false
0 ?? 'huli'  / / 0
Copy the code

  2. Logical null assignment:?? =

    The logical null assignment operator (x?? = y) only if x is nullish (null or undefined).

    const a = { duration: 50}; a.duration ?? =10;
console.log(a.duration);
// expected output: 50a.speed ?? =25;
console.log(a.speed);
// expected output: 25
Copy the code

  3. Logic or: | |

    If there is truth, it is true

    const a = 3;
const b = -2;
console.log(a > 0 || b > 0);  // true
Copy the code

    Can be the value of false

    • null
    • undefined
    • NaN
    • "" 与 ' '
    • 0
    • false

  4. Logic or assignment: | | =

    Returns if it does, and assigns if it does not

    const a = { duration: 50.title: ' ' };

a.duration ||= 10;
console.log(a.duration);
// expected output: 50

a.title ||= 'title is empty.';
console.log(a.title);
// expected output: "title is empty"
Copy the code

  5. Logic and: &&

    If both exist, it is true

    const a = 3;
const b = -2;

console.log(a > 0 && b > 0);
// expected output: false
Copy the code

  6. Logic and assignment: &&=

    If it exists, it is assigned

    let a = 1;
let b = 0;

a &&= 2;
console.log(a);
// expected output: 2

b &&= 2;
console.log(b);
// expected output: 0
Copy the code

  7. Optional chain operators:? .

    The optional chain operator (? .) allows you to read the value of a property located deep in the chain of connected objects without explicitly validating that each reference in the chain is valid. ? The. Operator functions like the. Chain operator, except that it does not cause errors when references are nullish (null or undefined), and the short-circuit returns undefined. When used with a function call, returns undefined if the given function does not exist.

    const adventurer = {
  name: 'Alice'.cat: {
    name: 'Dinah'}};constdogName = adventurer.dog? .name;console.log(dogName);
// expected output: undefined

console.log(adventurer.someNonExistentMethod? . ());// expected output: undefined
Copy the code