使用带有嵌套 Javascript 对象的变量
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Using variables with nested Javascript object
提问by Ben Flynn
Suppose I have this:
假设我有这个：
var a = { A : { AA : 1 }, B : 2 };
Is there a way for me to create a variable that could allow me to reference either AA or B? What would the syntax look like?
有没有办法让我创建一个可以让我引用 AA 或 B 的变量？语法会是什么样的？
// I know I can do this:
a['B']; // 2
a['A']['AA']; // 1
// something like this?
var myRef = ???;
a[myRef]; 1 or 2 depending on myRef
If not, what's a better way to get what I'm going for here?
如果没有，有什么更好的方法来获得我想要的东西？
回答by Krizz
Not directly.
不直接。
Solution 1 - use object flattening
解决方案 1 - 使用对象展平
Flatten object, to have new object var a = { 'A.AA' : 1; B : 2 };.
展平对象，以拥有新对象var a = { 'A.AA' : 1; B : 2 };。
See compressing object hierarchies in JavaScriptor Flattening a complex json object for mvc bindingto get the javascript function for it.
请参阅在 JavaScript 中压缩对象层次结构或为 mvc 绑定扁平化复杂的 json 对象以获取其 javascript 函数。
Soution 2 - write key-path accessor
解决方案 2 - 编写密钥路径访问器
I can see it was already addressed by Eugen. Reposted code-reviewed version:
我可以看到 Eugen 已经解决了这个问题。重新发布的代码版本：
function Leaf(obj,path) {
path=path.split('.');
var res=obj;
for (var i=0;i<path.length;i++) res=res[path[i]];
return res;
}
Solution 3 - use eval
解决方案 3 - 使用 eval
var x = eval("a." + myRef); // x will be 1 for myRef == "A.AA", 2 for "B"
Be careful with this solution as you may introduce some security issues. It is more of the curiosity.
小心使用此解决方案，因为您可能会引入一些安全问题。更多的是好奇心。
回答by Maximiliano Cespedes
Since i also encounter this problem, i wrote also a one line util for this (ES6):
由于我也遇到了这个问题，我也为此写了一个单行工具（ES6）：
const leaf = (obj, path) => (path.split('.').reduce((value,el) => value[el], obj))
Example:
例子：
const objSample = { owner: { name: 'Neo' } };
const pathSample = 'owner.name';
leaf(objSample, pathSample) //'Neo'
回答by Eugen Rieck
function Leaf(obj,path) {
path=path.split('.');
var res=obj;
for (var i=0;i<path.length;i++) obj=obj[path[i]];
return res;
}
Leaf(a,'B')=2
叶(a,'B')=2
Leaf(a,'A.AA')=1
叶(a,'A.AA')=1
Decorate with error handling etc. according to your needs.
根据您的需要使用错误处理等进行装饰。
回答by andy petrella
Actually no, because js object are seen as property bags and doing a[X]is for accessing first level properties only...
实际上不是，因为 js 对象被视为属性包，并且a[X]仅用于访问第一级属性......
But you could wrap the logic a['A']['AA']; // 1in a function that does the same, like this
但是您可以将逻辑包装 a['A']['AA']; // 1在一个功能相同的函数中，就像这样
//WARN... no undefined check here => todo !
function _(o, path) {
var tmp = o
for (var i=0 ; i < path.length ; i++) {
tmp = tmp[path[i]]
}
return tmp
}
var r = _(a, ['A', 'AA'])
This is pretty much the same as other answers, but the difference is when dummy boy create object property name containing dots... Like var a = {"a.a" : 3 }is valid.
这与其他答案几乎相同，但不同之处在于当虚拟男孩创建包含点的对象属性名称时...... Likevar a = {"a.a" : 3 }是有效的。
Now, such problem would occurs maybe more often now with the help of IndexedDB to store anything locally...
现在，在 IndexedDB 的帮助下，这样的问题可能会更频繁地发生在本地存储任何东西......
回答by Agustí Sánchez
With lodash _.get function, you can access nested properties with dot syntax.
使用 lodash _.get 函数，您可以使用点语法访问嵌套属性。
Node server-side example:
节点服务器端示例：
const _ = require('lodash');
let item = { a: {b:'AA'}};
_.get(item, 'a.b');
