在 Typescript 中,我检查对象的属性是否为空,如下所示:
var addressCountryName = response.address == null
? null
: response.address.country == null ? null : response.address.country.name;
地址和国家都可以为空...我也试过:
var addressCountryName = response.address?.country?.name;
这似乎行不通......
是否有检查 null/undefined 的最短方法?
最佳答案
目前没有null coalescing operator在 JavaScript 中。有不同的方法来解决它(比如嵌套的三元类型)。如果您愿意将辅助类型和函数推送到某个库中,您可以这样做:
type MyResponse = {
address?: null | {
country?: null | {
name?: null | string
}
}
}
let response: MyResponse = Math.random() < 0.5 ?
{ address: { country: { name: "France" } } } : { address: null }
var addressCountryName = nullSafe(response, r => r.address.country.name);
// string | undefined | null
nullSafe()
定义如下:
interface NullSigil {
[k: string]: NullSigil;
}
// phantom property to recover T from NullSafe<T>
type OriginalTypeKey = "***originalType***"
type IsNullable<T, Y, N> = null extends T ? Y :
undefined extends T ? Y : N;
type NullSafe<T, N = NullSigil> = Record<OriginalTypeKey, T> & (
T extends object ? {
[K in keyof T]-?: NullSafe<T[K], N>
} : IsNullable<T, NonNullable<T> | N, T>
)
type NullUnsafe<T> =
T extends Record<OriginalTypeKey, infer U> ? U :
T extends NullSigil ? null :
T
function nullSafe<T, U>(
val: T,
fn: <N extends NullSigil>(nullSafeVal: NullSafe<T, N>) => U
): NullUnsafe<U>;
function nullSafe(val: any, fn: (nullSafeVal: any) => any): any {
const nullSigil: NullSigil = new Proxy({} as NullSigil, { get(t, p, r) { return r } });
const deproxify = Symbol("deproxify");
function ns<T>(obj: T): NullSafe<T>;
function ns(obj: any) {
if ((typeof obj === "undefined") || (obj === null)) return nullSigil;
if (typeof obj !== "object") return obj;
return new Proxy(obj, { get(t, p, r) { return (p === deproxify) ? t : (p in t) ? ns(t[p]) : nullSigil } });
}
const ret: any = fn(ns(val));
if (ret === nullSigil) return null;
if (typeof ret !== "object") return ret;
return ret[deproxify];
}
是的,一团糟,这就是为什么我说要把它塞进图书馆。它通过制作 Proxy
来工作它始终允许您深入了解属性,即使它本质上是空的。
无论如何,这是一种选择。祝你好运!
关于typescript - 检查对象的属性在 Typescript 中是否为空,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/54354340/