JavaScript 如何连接两个 null 或 undefined 并返回 null

Question

假设值 firsName 和 lastName 来自某个数据源。该值有时可能都是 null 或都是未定义的。 fullName 将两者连接起来。

let a = {};
let b = {
    fullName: a && a.firstName+' '+a.lastName
};
console.log("fullName is "+JSON.stringify(b.fullName)); // fullName is "undefined undefined"

a = {
    firstName: null,
    lastName: null
};
b = {
    fullName: a.firstName+' '+a.lastName
};
console.log("fullName is "+JSON.stringify(b.fullName)); // fullName is "null null"

b = {
    fullName: {...a.firstName, ...' ', ...a.lastName}
};
console.log("fullName is "+JSON.stringify(b.fullName)); // fullName is {"0":" "}

b = {
    fullName: {...a.firstName, ...a.lastName}
};
console.log("fullName is "+JSON.stringify(b.fullName)); // fullName is {}

我目前的解决方案是

const getFullName = (firstName, lastName ) => {
    if ((typeof firstName == "undefined" || firstName === null) && (typeof lastName == "undefined" || lastName === null)) {
            return null;
    }
    else { 
        return firstName+' '+lastName
    }
}

b = {
    fullName: getFullName(a.firstName, a.lastName)
};
console.log("fullName with function is "+JSON.stringify(b.fullName)); // fullName with function is null

a = {};
console.log("fullName with function is "+JSON.stringify(b.fullName)); // fullName with function is null

有没有更好的方法使 b.fullName 的值为 null(无需编写函数)？

Answer 1

以下将是更好的解决方案:

return [firstName, lastName].filter(it => !!it).join(" ") || null

请注意，这还将包括“”作为 null/undefined，如果您只提供一个而不提供另一个，请避免在字符串中包括“null”。一般来说，这可能是您正在编写的函数所需要的。

例如:getFullName("John", null) 将返回“John”