TextMesh in WebGL

I am meeting an issue when using TextMesh and displaying it on a WebGL build. I got a NullReferenceException and the error message below:

 Can't add component because '' is not derived from Component.

However, the text displays properly on the Game view in Unity.

Below is how I created the text object via code.

 GameObject textObject = new GameObject ();
 textObject.AddComponent<TextMesh> ();
 textObject.GetComponent<TextMesh> ().text = text;
 textObject.GetComponent<TextMesh> ().color = fontColor;
 textObject.transform.parent = parentObject.transform;

Note that I am using 'Screen Space - Camera' on my Canvas, and parentObject is in canvas.

Will appreciate advice. Thanks!