从两层深层对象中提取价值

Question

I am trying to retrieve one particular value from within a two-levels deep object data structure. First off, though, I am saving into a variable within the function, like this:

getTargetId() {
    if (this.authenticationService.isAuthenticated()) {
        const userInfo = sessionStorage.getItem('currentUser');
        console.log(userInfo);
    }
}

From:

console.log(userInfo);

I get this back in the console:

{"token":"sometoken.value","data":{"_id":"8cd0362c0", "phone":"555-4343"...}

What I want to do is specifically pull out the "_id" value here.

I tried:

console.log(userInfo.data._id);

But then my IDE is showing me an error:

'Property '_id' does not exist on type 'string'.

How do I dig out "_id" in this case?

Answer 1

You are accessing it wrong
Try userInfo.data._id
In the log of your object you can see by the {} notation that data is another object, so after accessing data you can access its properties just as you would with any other object.

I also see that you are getting

'Property '_id' does not exist on type 'string'.

This could mean that you never parsed the information. To find out if this is the case this should be right:

Running->

console.log(userInfo);

Returns->

{"token":"sometoken.value","data":{"_id":"8cd0362c0", "phone":"555-4343"...}

Just after this code:
Running->

console.log(typeof userInfo);

Returns->

"string"

With your edits, I can see that this is the case.
Try:

userInfo = JSON.parse(sessionStorage.getItem('currentUser') );
console.log(userInfo.data._id);

Answer 2

The _id property is under the data key:

 const response = { "token":"sometoken.value", "data": { "_id":"8cd0362c0", "phone":"555-4343" } }; console.log(response.data._id) 

You can also use destructuring:

const { _id } = response.data;
console.log(_id)

or:

const { data: { _id }} = response;
console.log(_id);

Answer 3

So, as @jonsharpe pointed out, the key was to JSON.parse the string first. So this gets me the value I need for "_id":

getTargetId() {
    if (this.authenticationService.isAuthenticated()) {
        const userInfo = JSON.parse(sessionStorage.getItem('currentUser'));
        console.log(userInfo.data._id);
    }
}

Answer 4

Actually your string is returned as JSON string. So you have to parse it into object using JSON.parse() if you are using js or with $.parseJSON() if you are using Jquery. So your updated code now looks like this.

 var user ='{"token":"sometoken.value","data":{"_id":"8cd0362c0", "phone":"555-4343"}}'; var k = JSON.parse(user); alert(k.data._id); 

And Fiddle is here . Thank You