Using a if/else condition in a Cloud Firestore query

Question

I've written these scripts to run a function conditioned on the values of an HTTP GET request. The history var is defined correctly when I run two tests on the page:

1. history == 0
2. history == 1

The problem is allMessage function will always run, whether the value is 0 or 1 .

If I try to reverse the function ( limitMessage() on the if branch, allMessage() on the else branch) limitMessage() is the one that runs. I have no idea why the if else condition doesn't work as expected.

//*if else condition*

var history = "<? php echo isset($_GET['history']) ? $_GET['history'] : 0; ?>";
if (history != 1) {
  allMessage();
} else {
  limitMessage();
}

//*limitMessage*

function limitMessage() {
  firebase
    .firestore()
    .collection(collection)
    .doc(doc)
    .collection(collection)
    .orderBy("time", "desc")
    .limit(10)
    .onSnapshot(function (querySnapshot) {
      querySnapshot
        .docChanges()
        .reverse()
        .forEach(function (change) {
          var data = {
            id: change.doc.id,
            a: change.doc.data().a,
            b: change.doc.data().b,
            c: change.doc.data().c,
            d: change.doc.data().d,
            e: change.doc.data().e,
            f: change.doc.data().f,
          };

          if (change.type === "added") {
            msgData(data);
          }
          if (change.type === "modified") {
            msgData(data);
          }
        });
    });
}

//*allMessage*

function allMessage() {
  firebase
    .firestore()
    .collection(collection)
    .doc(doc)
    .collection(collection)
    .orderBy("time", "asc")
    .onSnapshot(function (querySnapshot) {
      querySnapshot.docChanges().forEach(function (change) {
        var data = {
          id: change.doc.id,
          a: change.doc.data().a,
          b: change.doc.data().b,
          c: change.doc.data().c,
          d: change.doc.data().d,
          e: change.doc.data().e,
          f: change.doc.data().f,
        };

        if (change.type === "added") {
          msgData(data);
        }
        if (change.type === "modified") {
          msgData(data);
        }
      });
    });
}

Answer 1

It is good practice to check the output of var by using typeof .

You can then decide how to manage the if/else statement.

You might not be handling the output correctly and why it is always running, whether the value is 0 or 1.

console.log(typeof 'checkme');
// expected output: "string"

console.log(typeof 12);
// expected output: "number"

console.log(typeof undeclaredVariable);
// expected output: "undefined"

console.log(typeof true);
// expected output: "boolean"

It can be confusing to write good if/else statements. To make it easier, I use if as equal to rather than not equal as I find it more intuitive when reading code and spotting issues.

var history=1;
if (history == 1) {
    console.log("yes");
} else {
    console.log("no");
}

Here are some of the comparison operators to try:

+-----------+-----------------------------------+-----------+---------+
| ==        | equal to                          | 5 == 8    | false   |
|           |                                   | 5 == 5    | true    |
|           |                                   | 5 == "5"  | true    |
| ===       | equal value and equal type        | 5 === 5   | true    |
|           |                                   | 5 === "5" | false   |
| !=        | not equal                         | 5 != 8    | true    |
| !==       | not equal value or not equal type | 5 !== 5   | false   |
|           |                                   | 5 !== "5" | true    |
|           |                                   | 5 !== 8   | true    |
+-----------+-----------------------------------+-----------+---------+