如何顯示JSON數組的一部分？

Question

我怎麼只能說明這部分

/DB/User_DataDb/61500546-4e63-42fd-9d54-b92d0f7b9be1這整個

對象obj.sel_an的：

[ 
    { 
     "__zone_symbol__state":true, 
     "__zone_symbol__value":"/db/User_DataDb/61500546-4e63-42fd-9d54-b92d0f7b9be1" 
    } 
] 

我寫了

console.log("obj.sel_an: ", 
JSON.stringify(this.sel_and.__zone_symbol__value)) 

而控制檯顯示t他的錯誤：'obj.sel_an：undefined。'

Answer 1

@Misaz here is my answer I talked about in the last comment.

Here is a section or rather a part of my code

db.Coll1.find() 
     .equal('id', and.id) 
.resultList(result => { 
       result.forEach(db1 => { 
        if (db1.sel_and === null) { 
        db1.sel_and = new Set();                 
       } 

       if (db1.sel_an === null) { 
        db1.sel_an = new Array(); 
       } 


db1.sel_an.push(promise1); // here is a JsonArray 
db1.sel_and.add(promise1); // here is a Set() 



    var db_child: any; 
    db_child = db1.sel_and.forEach(function (child) {console.log(child[0].__zone_symbol__value) }); 
    console.log(" db1.sel_and: ", db_child); 
    return db1.update({ refresh: true }); 
    }); 

Here is the result by JsonArray

1. By db1.sel_an.push(promise1);
   save in collection

   [ { "__zone_symbol__state": true, "__zone_symbol__value": "/db/User_DataDb/f6fe3fe3-17f1-49d8-83c3-b36dda42026d" } ]

Console output:

ZoneAwarePromise {__zone_symbol__state: null, __zone_symbol__value: Array(0)} 
    __zone_symbol__state:true 
    __zone_symbol__value:"/db/User_DataDb/d79ef084-17fc-441c-a8eb-13ba0a14f083" 
    __proto__:Object 

這裏是集（）

的結果 - >「db1.sel_and.add（承諾1）;「 - >保存爲[null]收藏N，但它應該被保存爲 - >[ 「/分貝/ User_DataDb/f55bf96d-2cb9-467f-8aa8-d60aced32fcf」]

Set(1) {ZoneAwarePromise {__zone_symbol__state: true, __zone_symbol__value: "/db/User_DataDb/f55bf96d-2cb9-467f-8aa8-d60aced32fcf"}} 
    size:(...) 
    __persistedSize__:1 
    __persistedState__:Object 
    __proto__:Set 
    [[Entries]]:Array(1) 
    0:null 
    length:1 

3.  

db_child = db1.sel_and.forEach(function (child) { console.log(child[0].__zone_symbol__value) }); 
    console.log(" db1.sel_and: ", db_child); 

I tried it with child[0].__zone_symbol__value But I got errors:

Uncaught (in promise): TypeError: Cannot read property '__zone_symbol__value' of undefined 
TypeError: Cannot read property '__zone_symbol__value' of undefined 
    at http://localhost:3000/main.bundle.js:28348:116 
    at Set.forEach (native) 
    at http://localhost:3000/main.bundle.js:28348:69 
    at Array.forEach (native) 
    at http://localhost:3000/main.bundle.js:28336:44 
    at ZoneDelegate.invoke (http://localhost:3000/polyfills.dll.js:4341:26) 
    at Object.onInvoke (http://localhost:3000/vendor.dll.js:30326:37) 
    at ZoneDelegate.invoke (http://localhost:3000/polyfills.dll.js:4340:32) 
    at Zone.run (http://localhost:3000/polyfills.dll.js:4133:43) 
    at http://localhost:3000/polyfills.dll.js:4720:57 
    at ZoneDelegate.invokeTask (http://localhost:3000/polyfills.dll.js:4374:31) 
    at Object.onInvokeTask (http://localhost:3000/vendor.dll.js:30317:37) 
    at ZoneDelegate.invokeTask (http://localhost:3000/polyfills.dll.js:4373:36) 
    at Zone.runTask (http://localhost:3000/polyfills.dll.js:4173:47) 
    at drainMicroTaskQueue (http://localhost:3000/polyfills.dll.js:4553:35) 
    at ZoneTask.invoke (http://localhost:3000/polyfills.dll.js:4431:25) 

If I don’t write [0] at the end of child, I get 「undefined」.If I written child.__zone_symbol__value, I get wrong . How can I leave out the 「[0].__zone_symbol__value」 without getting an error? Is it possible at all?

由於