set if unique

setu.js

function setu(node, item){
        let unique = true
        node.map().once(function (data) {
            let aProps = Object.getOwnPropertyNames(data);
            let bProps = Object.getOwnPropertyNames(item);
            // number of properties
            if (aProps.length === bProps.length) {
                console.log("same len")
                for (let i = 0; i < aProps.length; i++) {
                    let propName = aProps[i];
                    // values of same property
                    if (a[propName] === b[propName]) {
                        console.log("match")
                        unique = false
                    }
                }
            }
        })
        .then(function(){
            if(unique){
                node.set(item)
            }
            console.log(unique)
        })
    }