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ReferenceError: Must call super constructor in derived class before accessing 'this' or returning from derived constructor (V8-based)
ReferenceError: must call super constructor before using 'this' in derived class constructor (Firefox)
ReferenceError: 'super()' must be called in derived constructor before accessing |this| or returning non-object. (Safari)

ReferenceError

super() new 1 1 this this this this super()

class Base {
  constructor() {
    this.x = 1;
  }
}

class Derived extends Base {
  constructor() {
    console.log(this.x);
    //  Base this.x 
    // ReferenceError: must call super constructor before using 'this' in derived class constructor
  }
}

class Base {
  constructor() {
    this.x = 1;
  }
}

class Derived extends Base {
  constructor() {
    super();
    console.log(this.x); // 1
  }
}

super

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MDN 2026523

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JavaScript
JavaScript
1. (+)
2. (+=)
3. (=)
4. async function
5. async function*
6. await
7. (&)
8. (&=)
9. (~)
10. (|)
11. (|=)
12. (^)
13. (^=)
14. class
15. (,)
17. (--)
18. delete
20. (/)
21. (/=)
22. (==)
23. (**)
24. (**=)
25. function
26. function*
27. (>)
28. (>=)
29. ( )
30. import.meta
  1. import.meta.resolve()
31. import()
32. in
33. (++)
34. (!=)
35. instanceof
36. (<<)
37. (<<=)
38. (<)
39. (<=)
40. (&&)
41. (&&=)
42. (!)
43. (||)
44. (||=)
45. (*)
46. (*=)
47. new
48. new.target
49. null
50. (??=)
51. (??)
54. (?.)
56. (%)
57. (%=)
58. (>>)
59. (>>=)
60. (...)
61. (===)
62. (!==)
63. (-)
64. (-=)
65. super
66. this
67. typeof
68. (-)
69. (+)
70. (>>>)
71. (>>>=)
72. void
73. yield
74. yield*