一、变量声明let、const
/** * @变量声明 */ "use strict" // 1.变量越域 { var a = 1; let b = 2; } console.log(a);// 1 console.log(b);// b is not defined // 2.不可多次声明同一变量 var x = 0; var x = 1; let y = 2; let y = 3; console.log(x);// Identifier 'y' has already been declared // 3.var变量提升 console.log(m); var m = 10;// undefined console.log(n); // Cannot access 'n' before initialization let n = 10; // 4.常量const,必须初始化,且不可改值 const k = 5; k = 6;// Assignment to constant variable.
二、解构表达式
三、函数优化
四、对象优化
五、Promise