Javascript join multiple arrays with & but I get duplicates

I have this project in which I create a link with multiple arrays that are joined with & signs. It works perfectly, but when I get more than 3 arrays, it doesn’t. When I skip a couple of questions I get a & sign at the beginning of the string and when I only choose the first it adds one to the end which is bad. Also if I choose the first and the last array and skip the rest there a multiple & added between while I always just want 1.

I use this to join the arrays:

/**
         * Returns the parameters for the URL.
         *
         * @returns {string}
         */
        getLink() {
            this.tmp = [];
            for (let i = 0; i < this.url.length; i++) {
                // Check if question is from the same quiz part and adds a , between chosen answers and add the right prefix at the beginning
                if (this.url[i].length > 0) {
                    this.tmp.push("" + Quiz[i].prefix + this.url[i].join(","))
                }
                // if the link is empty remove everything that was added (& an ,)
                if (this.url[i].length === 0) {
                    this.tmp.push("");
                }
            }
            /// If answers are from different quiz parts add a & between answers
            return "" + this.tmp.join("&");
        }

Quiz and this.url are the arrays and .prefix and stuff are keys of the arrays.

This is what I use to check the link string to remove the unwanted & signs:

        LinkChecker(link) {
            let cleanLink = link.split('&&').join('&');
            if (cleanLink[0] === '&') {
                cleanLink = cleanLink.slice(1);
            }
            if (cleanLink[cleanLink.length - 1] === '&') {
                cleanLink = cleanLink.slice(0, -1);
            }
            return cleanLink;
            console.log(cleanLink.length)
        }

And this is something I tried now:

            let i = 0;
            let LastLink = '';
            let FirstLink = LastLink;
            let link = this.LinkChecker(this.getLink());
            if (link[link.length -1] === '&'){
                LastLink = link.slice(0, -1);
            }
            while(i == '&'){
                if(LastLink[i] === '&'){
                    FirstLink = link.slice(-1, 0);
                }
                i++
            }
            console.log(FirstLink)

But it also doesn’t really work.

Preview:

bd_shoe_size_ids=6621&&&

&&manufacturer_ids=5866

bd_shoe_size_ids=6598&&&manufacturer_ids=5866

It’s supposed to look like:

bd_shoe_size_ids=6598&manufacturer_ids=5866

Answer

It is better to avoid than to fix (the double &).

Remove the whole block that does push(""). This push is adding an entry to your array that you really don’t want to have at all, so just don’t push it.