ReferenceError: Can't find variable: i （for循环问题）

Question

I made a break from my react native project for about 3 weeks and now I came back and wanted to work on it, unfortunaly the app doesnt even render the first screen components. I already figured out what the problem is, Im just totaly confused what is going on:

    var chatkeys = [];
    var partnerkeys = [];
    var contactsDATA = [];

    await firebase.database().
    ref(`users/${PersonalId}/chats`).
    once('value').
    then(snapshot =>{
        for (i in snapshot.val()){//pulling all chatcodes out of database and pushing into chatkeys
            chatkeys.push(snapshot.val()[i]);
        };
    });

The problem is located in the for-loop. Here is the error Im receiving:

[Unhandled promise rejection: ReferenceError: Can't find variable: i]

• node_modules\react-native\node_modules\promise\setimmediate\core.js:37:13 in tryCallOne
• node_modules\react-native\node_modules\promise\setimmediate\core.js:123:24 in setImmediate$argument_0
• node_modules\react-native\Libraries\Core\Timers\JSTimers.js:130:14 in _callTimer
• node_modules\react-native\Libraries\Core\Timers\JSTimers.js:181:14 in _callImmediatesPass
• node_modules\react-native\Libraries\Core\Timers\JSTimers.js:441:30 in callImmediates
• node_modules\react-native\Libraries\BatchedBridge\MessageQueue.js:387:6 in __callImmediates
• node_modules\react-native\Libraries\BatchedBridge\MessageQueue.js:135:6 in __guard$argument_0
• node_modules\react-native\Libraries\BatchedBridge\MessageQueue.js:364:10 in __guard
• node_modules\react-native\Libraries\BatchedBridge\MessageQueue.js:134:4 in flushedQueue

• [native code]:null in flushedQueue
• [native code]:null in callFunctionReturnFlushedQueue

How can JS not find the variable "i"? I never told JS to search for "i" - it's just supposed to be a counter to loop through the whole snapshot.val() array. What is going on here?

Answer 1

The error states that i is not defined. reading your code, I can see that i inside your for loop declaration may be missing the let i variable.

Have you tried for (let i in snapshot.val()){

Answer 2

i is not declared in the scope. Try

for (let i in snapshot.val()){//pulling all chatcodes out of database and pushing into chatkeys
            chatkeys.push(snapshot.val()[i]);
        };

OR

let i;
for (i in snapshot.val()){//pulling all chatcodes out of database and pushing into chatkeys
            chatkeys.push(snapshot.val()[i]);
        };

Answer 3

I made a break from my react native project for about 3 weeks and now I came back and wanted to work on it, unfortunaly the app doesnt even render the first screen components. I already figured out what the problem is, Im just totaly confused what is going on:

    var chatkeys = [];
    var partnerkeys = [];
    var contactsDATA = [];

    await firebase.database().
    ref(`users/${PersonalId}/chats`).
    once('value').
    then(snapshot =>{
        for (i in snapshot.val()){//pulling all chatcodes out of database and pushing into chatkeys
            chatkeys.push(snapshot.val()[i]);
        };
    });

The problem is located in the for-loop. Here is the error Im receiving:

[Unhandled promise rejection: ReferenceError: Can't find variable: i]

• node_modules\react-native\node_modules\promise\setimmediate\core.js:37:13 in tryCallOne
• node_modules\react-native\node_modules\promise\setimmediate\core.js:123:24 in setImmediate$argument_0
• node_modules\react-native\Libraries\Core\Timers\JSTimers.js:130:14 in _callTimer
• node_modules\react-native\Libraries\Core\Timers\JSTimers.js:181:14 in _callImmediatesPass
• node_modules\react-native\Libraries\Core\Timers\JSTimers.js:441:30 in callImmediates
• node_modules\react-native\Libraries\BatchedBridge\MessageQueue.js:387:6 in __callImmediates
• node_modules\react-native\Libraries\BatchedBridge\MessageQueue.js:135:6 in __guard$argument_0
• node_modules\react-native\Libraries\BatchedBridge\MessageQueue.js:364:10 in __guard
• node_modules\react-native\Libraries\BatchedBridge\MessageQueue.js:134:4 in flushedQueue

• [native code]:null in flushedQueue
• [native code]:null in callFunctionReturnFlushedQueue

How can JS not find the variable "i"? I never told JS to search for "i" - it's just supposed to be a counter to loop through the whole snapshot.val() array. What is going on here?