I’m learning Threejs by following this tutorial

I’m stuck at making the boilderplate. It got error: “Uncaught TypeError: Cannot read properties of undefined (reading ‘uniforms’).

In my code, i defined uniforms at:

<!-- language: lang-js -->
    addObjects() {
        this.material = new THREE.ShaderMaterial({
            vertexShader: vertex,
            fragmentShader: fragment,
            extensions: {
                derivatives:" #extension GL_OES_standard_derivatives: enable"
            },
            uniforms: {
                time: {value:0},
                resolution: {value: new THREE.Vector4()},
            },
            side: THREE.DoubleSide

        });
        this.geometry = new THREE.PlaneGeometry(1,1,1,1);

        this.plane = new THREE.Mesh(this.geometry, this.material);
        this.scene.add(this.plane);
    }

Then, i called it in this block:

<!-- language: lang-js -->
    render() {
        if(!this.isPlaying) return;
        this.time += 0.05;
        this.material.uniforms.time.value = this.time;
        requestAnimationFrame(this.render.bind(this));
        this.renderer.render(this.scene, this.camera);
    }

What seem to be the problems here?