Allow me to reply myself.
This question is actually about how to get an instance object’s class name.
The solutions are shown in the code below:
import * as tf from "@tensorflow/tfjs";

const a = tf.randomNormal([3, 4, 5]);
a.print();

console.log('type of a \t\t:', typeof(a));                      // returns a string     "object"
console.log('a is an instance of \t:', a instanceof tf.Tensor); // returns a boolean    "true"
console.log('constructor of a \t:', a.constructor);             // returns a function   "Tensor(){}"
console.log('constructor name of a \t:', a.constructor.name);   // returns a string     "Tensor"

// reference link : 
// https://stackoverflow.com/questions/1249531/how-to-get-a-javascript-objects-class?rq=1

function getNativeClass(obj) {
  if (typeof obj === "undefined") return "undefined";
  if (obj === null) return "null";
  return Object.prototype.toString.call(obj).match(/^\[object\s(.*)\]$/)[1];
}

function getAnyClass(obj) {
  if (typeof obj === "undefined") return "undefined";
  if (obj === null) return "null";
  return obj.constructor.name;
}

console.log('getAnyClass of a \t:', getAnyClass(a));        // returns a string   "Tensor"
console.log('getNativeClass of a \t:', getNativeClass(a));  // returns a string   "object"

[codeSandBox link 1]
[stackoverflow reference link 2]