javascript prototype definition error

Question

I have this function(class) which I define a prototype function.

function testit(t,l, w, h, c, p) {
    this.div;
    this.obj = { "top": t, "left": l, "width": w, "height": h, "color": c };
}

testit.prototype.showit = function () {
     this.div = $("<div />")
        .css({
            "position": "absolute",
            "top": this.obj.top,
            "left": this.obj.left,
            "width": this.obj.width,
            "height": this.obj.height,
            "border": "1px solid " + this.obj.color
        })
        .appendTo(p);
}

When running the following code -

var aa;

aa = new testit(100, 100, 100, 100, "#CCCCCC", "body");
aa.showit();

I get the following error -

Unhandled exception

What is wrong with the prototype definition ?

Where are you instantiating `testit` in relation to the class definition? — wmash, Mar 04 '18 at 16:54
After defining `p`, there was no problem with your code for me — vityavv, Mar 04 '18 at 16:56

T.J. Crowder · Accepted Answer · 2018-03-04T17:09:34.173

The code doesn't cause the error you've listed (see the snippet I added to your question), unless of course you have a global p variable that's not a string or DOM element, which case I suppose it could.

It does have a different error: p is not defined at the point you use it. You need to remember p in the constructor (this.p = p; perhaps) and then use that property (this.p) when calling appendTo:

function testit(t,l, w, h, c, p) {
    this.div;
    this.obj = { "top": t, "left": l, "width": w, "height": h, "color": c };
    this.p = p;
}

testit.prototype.showit = function () {
     this.div = $("<div />")
    .css({
        "position": "absolute",
        "top": this.obj.top,
        "left": this.obj.left,
        "width": this.obj.width,
        "height": this.obj.height,
        "border": "1px solid " + this.obj.color
    })
    .appendTo(this.p);
}

var aa;

aa = new testit(100, 100, 100, 100, "#CCCCCC", "body");
aa.showit();

<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>

You'll also have to beware of this issue if you're calling showit in (say) an event callback.

javascript prototype definition error

1 Answers1