Typescript: Avoid comparison by reference

Question

I need to store a list of points and check if a new point is already included in that list ``` class Point { x: number; y: number; constructor(x: number, y: number) { this.x = x; this.y = y; } } window.onload = () => { var points : Point[] = []; points.push(new Point(1,1)); var point = new Point(1,1); alert(points.indexOf(point)); // -1 } ``` Obviously typescript uses comparison by reference but in this case that doesn't make sense. In Java or C# I would overload the `equals` method, in typescript that doesn't seem to be possible. I considered to loop through the array with `foreach` and check each entry for equality, but that seems rather complicated and would bloat the code. Is there something like `equals` in typescript ? How can I implement my own comparisons ?

Accepted Answer

You could wrap the collection in a `PointList` that only allows `Point` objects to be added via an `add` method, which checks to ensure no duplicates are added.

This has the benefit of encapsulating the "No duplicates" rule in a single place, rather than hoping that all calling code will check before adding a duplicate, which would duplicate the rule in many places.

```
class Point {
    constructor(public x: number, public y: number) {
    }
}

class PointList {
    private points: Point[] = [];

get length() {
        return this.points.length;
    }

add(point: Point) {
        if (this.exists(point)) {
            // throw 'Duplicate point';
            return false;
        }

this.points.push(point);
        return true;
    }

exists(point: Point) {
        return this.findIndex(point) > -1;
    }

findIndex(point: Point) {
        for (var i = 0; i < this.points.length; i++) {
            var existingPoint = this.points[i];
            if (existingPoint.x === point.x && existingPoint.y === point.y) {
                return i;
            }
        }

return -1;
    }
}

var pointList = new PointList();

var pointA = new Point(1, 1);
var pointB = new Point(1, 1);
var pointC = new Point(1, 2);

pointList.add(pointA);
alert(pointList.length); // 1

pointList.add(pointB);
alert(pointList.length); // 1

pointList.add(pointC);
alert(pointList.length); // 2
```

Typescript: Avoid comparison by reference

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