let a = null;
let b = 2;
b = a ?? b;
console.log(b);//2
let a = 3;
let b = a ?? 5;
console.log(b);//3
语法格式为a ?? b。其意义为:当a为 null 或者 undefined 时,返回b的值,否则返回a的值;
let a = null;
let b = 2;
b = a ?? b;
console.log(b);//2
let a = 3;
let b = a ?? 5;
console.log(b);//3
语法格式为a ?? b。其意义为:当a为 null 或者 undefined 时,返回b的值,否则返回a的值;