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1. 无效合并运算符
const name = null ?? 'John';console.log(name); // 输出: John
2.可选链接
const user = {name: '张三',address: {city: '四川',state: 'NY'}
};console.log(user?.address?.city); // 输出: 四川
console.log(user?.address?.zipCode); // 输出: undefined
3.判断输入框不为空
//bad
if(value !== null && value !== undefined && value !== ''){//...
}//good
if((value??'') !== ''){//...
}