get strokeLength() {
if ('getTotalLength' in this._el) {
return this._el.getTotalLength();
} else if (this._el instanceof SVGLineElement) {
return Math.sqrt(square(this._el.x2.baseVal.value - this._el.x1.baseVal.value) +
square(this._el.y2.baseVal.value - this._el.y1.baseVal.value));
} else {
let dim = this.bounds;
return 2 * dim.height + 2 * dim.width;
}
}
let sse = data.reduce((sum, d) => sum + square(d[1] - fn(d[0])), 0);
let ssyy = data.reduce((sum, d) => sum + square(d[1] - mean), 0);