JavaScript如何连接两个null或undefined并返回null

Question

假设值firsName和lastName来自某些数据源。该值有时可能为null或都未定义。fullName将两者结合在一起。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 {}我当前的解决方案是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 nulla = {};console.log("fullName with function is "+JSON.stringify(b.fullName)); // fullName with function is null有没有更好的方法来使b.fullName的值为null（无需编写函数）？

Answer 1

以下是更好的解决方案：

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

请注意，这还将在空/未定义中包含“”，并且如果您提供一个而不提供另一个，则避免在字符串中包含“ null”。通常，这对于您正在编写的功能可能是理想的。

例如：getFullName("John", null)将返回“约翰”

Answer 2

这是少数使用松散相等运算符（因为null和undefined彼此松散相等，但对别的枚举相等）有益的情况之一。然后，您可以将条件简化为：

const getFullName = (firstName, lastName ) => {

    if (firstName == null && lastName == null) {

        return null;

    } else { 

        return firstName + ' ' + lastName

    }

}