I have a JS/Svelte project fetching some data from an internal API endpoint. I can console.log() the value I need but not append it to an array. Can anybody help me? This is the code, this one works perfectly, giving me back the ID I need:

let tracks = []
async function createTrack(name, artists) {   
        const track_id = await fetch("/api/createtrack", {
            method: 'POST',
            body: JSON.stringify({  name: name,
                                    artists: artists,
                                    release: release._id
                                    })
            }).then((response) => response.json()).then((data) => {return data.id;});
        console.log(track_id)   
    }

but this doesn't, I can't append to the array:

let tracks = []
async function createTrack(name, artists) {   
        const track_id = await fetch("/api/createtrack", {
            method: 'POST',
            body: JSON.stringify({  name: name,
                                    artists: artists,
                                    release: release._id
                                    })
            }).then((response) => response.json()).then((data) => {return data.id;});
        tracks.push(track_id)   
    }