Javascript中对象属性的方法

Question

我有一个构造函数：

function Point(point, left, right) {
    this.p = point;
    this.l = left;
    this.r = right
}
var bezierPoint = new Point([0.0,0.0],[-50.43794, 0.0],[25.54714,4.78643])

有没有合适的方法来创建一个我可以在所有属性中使用而不是对象本身的方法？ 例如如果我想输出

console.log(bezierPoint.l) // -50.43794, 0.0
console.log(bezierPoint.l.round()) // -50, 0
console.log(bezierPoint.r.round()) // 26, 5

或者这是错误的方法，我应该为我将使用的数据类型制定新的方法？类似的东西

Array.prototype.round = function() {
    return [Math.round(this[0]), Math.round(this[1])] //this code doesn't matter now
}
console.log(bezierPoint.l.round()) // -50, 0

Answer 1

您可以将参数用作内部变量并公开方法如下：

function Point(point, left, right) {

    function exposed(points) {
        return {
            value: function () {
                return points;
            },
            round: function () {
                return [Math.round(points[0]), Math.round(points[1])];
            }
        };
    }

    this.p = exposed(point);

    this.l = exposed(left);

    this.r = exposed(right);

}

然后你可以像这样使用它：

var bezierPoint = new Point([0.0, 0.0], [-50.43794, 0.0], [25.54714, 4.78643]);

document.write('value:' + bezierPoint.l.value() + '<br />'); // value:-50.43794,0

document.write('round:' + bezierPoint.l.round() + '<br />'); // round:-50,0

Answer 2

另一种方法。更多代码，但更多原型和可靠。

// Common point class

/**
 * Creates simple point class
 * Point can be passed as two separate coordinates or as an array (coordinates pair). In case of array, second argument is omitted.
 * @param {String|Number|Array} a
 * @param {String|Number|undefined} b
 * @returns {Point}
 */
var Point = function (a, b) {
    if (!!a && !!b) {
        this.a = parseFloat(a);
        this.b = parseFloat(b);
    } else if (a.constructor === Array ? a.length === 2 : false) {
        this.a = parseFloat(a[0]);
        this.b = parseFloat(a[1]);
    } else {
        throw 'Wrong data provided for `Point`';
    }
}

/**
 * @returns {Array} Rounded coordinates pair
 */
Point.prototype.round = function () {
    return [Math.round(this.a), Math.round(this.b)];
}

/**
 * @returns {Array} Raw coordinates pair (as they were passed to constructor)
 */
Point.prototype.value = function () {
    return [this.a, this.b];
}

// Bezier point class

/**
 * Creates a Bezier point instance
 * @param {Array|Point} point
 * @param {Array|Point} left
 * @param {Array|Point} right
 * @returns {BezierPoint}
 */
var BezierPoint = function (point, left, right) {
    this.p = point instanceof Point ? point : new Point(point);
    this.l = left instanceof Point ? left : new Point(left);
    this.r = right instanceof Point ? right : new Point(right);
}

// Operation

var bezierPoint = new BezierPoint([0.0,0.0], [-50.43794, 0.0], [25.54714,4.78643]);

每个点都可以作为数组传递给BezierPoint，也可以作为格式正确的Point 类。

---

UPD：作为对现有答案能力的扩展，可以提供下一种方式来定义任意点数。

var ArbitraryNumberOfPoints = function (args) {
    this.points = args.length === 0 ? [] :
        args.map(function (arg) {
            return arg instanceof Point ? arg : new Point(arg);
        });
}

ArbitraryNumberOfPoints.prototype.round = function () {
    return this.points.map(function (pointInstance) {
        return pointInstance.round();
    });
}