Firebase query endAt() except/exclude its key - firebase

Question

a
b
c
d
e
FirebaseRef.orderByKey().endAt('c').limitToLast(2) will return
b, c
I want to retreive except c, so a, b are what I want.
How can I do this?

Answer 1

In this case you need to use limitToFirst() method like this:
FirebaseRef.orderByKey().limitToFirst(2);
You output will be: a, b
If you have data before a, you need to startAt() and endAt methods like this:
FirebaseRef.orderByKey().startAt('a').endAt('b');
Please see the official documentation regarding Retrieving Data in Firebase

Answer 2

If your endAt() query uses strings, it will compare lexicographically, so you'll need to subtract one charCode from the last character of the string. The following should work when searching for strings:
FirebaseRef.orderByKey().endAt(exclude('c')).limitToLast(2) will return
exclude(key){
return key.substring(0, key.length - 1) + String.fromCharCode(key.charCodeAt(key.length - 1) - 1)
}

Answer 3

#godlerner's answer worked best for me however an edge case needs to be added because if you have a key that ends with a 0 it will replace the 0 with "/" which will cause the query to fail and throw an exception because firebase does not allow keys to contains "/"
This works better
exclude(key) {
let unallowedChars = '.#$/[]'
let newKey = key.substring(0, key.length - 1) + String.fromCharCode(key.charCodeAt(key.length - 1) - 1)
if(unallowedChars.includes(newKey[newKey.length - 1])){
while(unallowedChars.includes(newKey[newKey.length - 1])) {
newKey = newKey.substring(0, newKey.length - 1) + String.fromCharCode(newKey.charCodeAt(newKey.length - 1) - 1)
}
}
return newKey
}