Method _flattenStack

src/base/stack-mixin.js:198–203

()

    }

    _flattenStack () {
        // A round about way to achieve flatMap
        // When target browsers support flatMap, just replace map -> flatMap, no concat needed
        const values = this.data().map(layer => layer.domainValues);
        return [].concat(...values);
    }

    xAxisMin () {
        const m = min(this._flattenStack(), pluck('x'));