Is it possible to add a method dynamically in Javascript?

Question

Hey I am making a firebase database call that looks like this:

db.collection("posts").where("location", "==", location)
    .get().then((querySnapshot) => {
        [...]
    })

The user can specify from what countries he would like to get posts (the .where() method is for that). But he can also pick all the countries, so in that case the method is no longer needed. Is there a way to add methods dynamically?

Something like this:

db.collection("posts")if(location != "all"){.where("location", "==", location)}
    .get().then((querySnapshot) => {
        [...]
    })

Just put the function call inside a condition: let query = db.collection(...); if (...) query = query.where(...); query.get().then(...) — CherryDT
– CherryDT, Commented Oct 4, 2021 at 19:22

Yury Tarabanko · Accepted Answer · 2021-10-04 19:23:57Z

2

You can use a function

const addLocationCondition = (collection, location) => 
    location === "all" ? collection : collection.where('location', '==', location);

addLocationCondition(db.collection('posts'), location).get()...

answered Oct 4, 2021 at 19:23

Yury Tarabanko

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2 Comments

Reality Over a year ago

A shorter alternative than an if statement, as well as a cleaner alternative to the other answers. I like it!

Yury Tarabanko Over a year ago

@Reality "Make const not var". :) It will look even better if/when this proposal got adopted github.com/tc39/proposal-pipeline-operator db.collection('post') |> addLocationCondition(#, location) |> #.get() |> await

Barmar · Accepted Answer · 2021-10-04 19:25:24Z

1

No, you can't put a conditional there.

Just use if to decide whether to call .where().

let posts = db.collection("posts");
let filtered;
if (location == "all") {
    filtered = posts;
} else {
    filtered = posts.where("location", "==", location);
}
filtered.get().then(querySnapshot => { 
    // ...
});

answered Oct 4, 2021 at 19:25

Barmar

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Comments

enapupe · Accepted Answer · 2021-10-04 19:27:00Z

1

I'm not completely sure about this db API but this should work:

let query = db.collection("posts")
if(location != "all"){
  query = query.where("location", "==", location)
}
query.get().then((querySnapshot) => {
   [...]
})

answered Oct 4, 2021 at 19:27

enapupe

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