JavaScript Expression笔记

Expressions

Member

• a.b

• a[b]

• foo`string`

  const w = 'world';
  function foo() {
      console.log(arguments); // [Arguments] { '0': [ 'Hello ', '' ], '1': 'world' }
  }
  foo`Hello ${w}`;
  

• super.a

  class Parent {
      constructor() {}
      eat() {
          return 'eat';
      }
  }
  
  class Child extends Parent {
      constructor() {
          super();
          console.log(super.eat());
      }
  }
  
  new Child(); // eat
  

• super['b']

• new.target

  function Foo() {
      console.log(new.target); // new.target 只能在函数里面使用
  }
  
  Foo(); // undefined
  
  new Foo(); // [Function: Foo]
  

  TIPS: 由此可见，new.target可用来判断是否被new调用

UpdateExpression

[no Lineterminator] ++

let a = 1;
let b = 2;
let c = 3;

a
++
b
++
c

console.log(a, b, c); // 1 3 4

TIPS: 此处a ++ ，a与++中间不能换行，否则语法不成立