JavaScript Function Constructor Methods

function VideoType(title, category, cast, price, qty, length) {
    this.title = title; // string
    this.category = category; // string
    this.cast = cast; //array
    this.price = price; //number
    this.qty = qty; //number
    this.length = length; //number

    // Setting a default value for the parameter inside the constructor = 5
    this.changeQtyBy = function(ChangingNumber = 5) {

        if (Number.isInteger(this.qty)) {
            return this.qty + ChangingNumber;
        } else {
            return this.qty - ChangingNumber;
        }
    }

    this.getCast = function() {
        return this.cast; // this one line just returns values of the array
    }

    this.toString = function() { // add born part maybe 
            return `${this.title}|| ${this.category}|| ${this.cast}|| ${this.price}|| ${this.qty}|| ${this.length}|| ${this.getCast()}|| ${this.changeQtyBy()}`;
        } //I added the methods in toString() method to display the results

} // end of the constructor


// calling this function body onload event
function startMeUp() {

    let videos = [];

    videos.push(new VideoType("Simba", "Cartoon", ["castItem1", "castItem2"], 25, 10, 50));
    videos.push(new VideoType("Taken", "Thriller", ["castItem5", "castItem6"], 20, 11, 40));
    videos.push(new VideoType("Execution", "Thriller", ["castItem3", "castItem4"], 15, 8, 30));
    videos.push(new VideoType("Kungfu", "Comedy", ["castItem7", "castItem8"], 18, 7, 20));

    for (var i = 0; i < videos.length; i++) {

        videos[i].qty += 1;
        // So it adds 1 to all the items of the qty property in the Object which is stored in the array videos. So we had to loop through it
        // to add 5 units to the qty property for all videos. You must use a for loop to do this
    }

    let outputElement = document.getElementById('divVideoOutput');
    // clears the output every time
    outputElement.innerHTML = "";

    for (let i = 0; i < videos.length; i++) {

        var tempVideo = videos[i]; //Instead of typing StoreItems[i] every time the array we need, we can assign to a variable and use that to refer
        var tempEL = document.createElement("p");
        tempEL.innerText += tempVideo.toString();
        //Append to the Div
        outputElement.appendChild(tempEL);
    } //end for loop

} // closing function startMeUP

// I didn't use the document.write as tried using .toString() method plus DOM createElement P and then appendChild instead 

console.log(changeQtyBy() );  and console.log(this.changeQtyBy() );