如何在JS中解析和访问JSON？

Question

When I did

console.log(JSON.parse(JSON.stringify(e)).data);

I got

{"deviceId":"1234","instanceId":"drogon","operationalEvent":"Shutdown","subEventReason":"Finished","operationalState":"in shutdown","createdAt":"2019-06-07 15:22:17","initiator":"system"}

When I did

console.log(JSON.parse(JSON.stringify(e)).data.deviceId);

I got

app.js:10254 undefined

What did I do wrong ?

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Updated - more info

console.log(typeof JSON.parse(JSON.stringify(e))) //object

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console.log(typeof JSON.parse(JSON.stringify(e)).data) //string

Answer 1

JSON.parse(JSON.stringify(e)) is nonsense, it's the same as just the original object e to begin with. Since you say that e.data is a string, that's what you need to parse:

let data = JSON.parse(e.data);
console.log(data.deviceId);

Answer 2

Try this

 let e= { data: `{"deviceId":"1234","instanceId":"drogon","operationalEvent":"Shutdown","subEventReason":"Finished","operationalState":"in shutdown","createdAt":"2019-06-07 15:22:17","initiator":"system"}` } console.log(JSON.parse(JSON.parse(JSON.stringify(e)).data).deviceId); 

Answer 3

JSON.parse(JSON.stringify(e)) is not non-sense as pointe above. It is used to remove object reference. You can try this

const data1 = JSON.parse(JSON.stringify(e)).data
const parsedData = JSON.parse(data1) // e.data is of type 'string' as you have pointed out
const deviceId = parsedData.deviceId