Assign class function to variable, no access to `this` variable?

Question

I want to assign variable to class function (like const func2 = this.play_1;), but after that func2 has no access to this property

function play_1(message = "play_1") {
  console.log("GLOBAL FUNCTION:", message);
}

class Demo {
  constructor() {
    this.number = 10;
  }

  play_1(message = "class play_1") {
    console.log("CLASS FUNCTION:", this.number, message);
  }

  test_assign_function() {
    play_1("without this");

    this.play_1("with this");

    const func = play_1;
    func("WORKING - func message from class is global");

    const func2 = this.play_1;
    func2("NOT WORKING - func message from class");
  }
}

function test_assign_function_in_class() {
  cls = new Demo();
  cls.test_assign_function("class message");
}

test_assign_function_in_class();

Get error:

"S:\Program Files\nodejs\node.exe" S:\!kyxa\!code\play_chrome_cdp\nodejs_1\!play\assing_function.js
GLOBAL FUNCTION: without this
CLASS FUNCTION: 10 with this
GLOBAL FUNCTION: WORKING - func message from class is global
S:\!kyxa\!code\play_chrome_cdp\nodejs_1\!play\assing_function.js:11
    console.log("CLASS FUNCTION:", this.number, message);
                                        ^

TypeError: Cannot read property 'number' of undefined
    at play_1 (S:\!kyxa\!code\play_chrome_cdp\nodejs_1\!play\assing_function.js:11:41)
    at Demo.test_assign_function (S:\!kyxa\!code\play_chrome_cdp\nodejs_1\!play\assing_function.js:23:5)
    at test_assign_function_in_class (S:\!kyxa\!code\play_chrome_cdp\nodejs_1\!play\assing_function.js:29:7)
    at Object.<anonymous> (S:\!kyxa\!code\play_chrome_cdp\nodejs_1\!play\assing_function.js:32:1)
    at Module._compile (internal/modules/cjs/loader.js:1063:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1092:10)
    at Module.load (internal/modules/cjs/loader.js:928:32)
    at Function.Module._load (internal/modules/cjs/loader.js:769:14)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:72:12)
    at internal/main/run_main_module.js:17:47