Uncaught TypeError: Cannot read property 'LineCap' of undefined

Uncaught TypeError: Cannot read property 'LineCap' of undefined

// 代码段

start: function () {
if (cc.director.setClearColor) {
cc.director.setClearColor( cc.hexToColor('#01aaff') );
}

    this.time = 0;

    this.ctx = this.getComponent("cc.Graphics");
    this.ctx.lineCap = cc.Graphics.LineCap.BUTT;
    this.ctx.lineJoin = cc.Graphics.LineJoin.ROUND;

    let waves = this.waves;
    for (let i = 0, l = waves.length; i < l; i++) {
        waves[i].waveFn = Waves[Waves.Enum[waves[i].waveType]].bind(Waves);
        waves[i].easeFn = Ease[Ease.Enum[waves[i].easeType]].bind(Ease);
    }
},