Class based component constructor and supper()

by

Summary

A common React error occurs when developers omit super() in class component constructors or misunderstand its purpose. The super() call is mandatory in JavaScript class constructors that define their own constructor and intend to use this. It initializes the parent class instance, making this available in the derived class. React enforces this rule because class components extend React.Component, and without super(), the component instance cannot be properly initialized.

Root Cause

The error happens because:

  • JavaScript ES6 class semantics require super() to be called before this can be used in a derived class constructor
  • When you define a constructor in a class that extends another class, you must call super() first
  • React’s Component class constructor expects to initialize the component instance, state, and internal properties
  • Without super(), the derived class has no valid this context to work with

Why This Happens in Real Systems

This issue commonly appears when:

  • Developers migrate from older React patterns (createClass) to ES6 classes
  • Teams enforce linting rules that flag unused variables (including unused super() parameters)
  • Code is auto-generated by scaffolding tools but is later modified incorrectly
  • Developers copy patterns from documentation without understanding the underlying JavaScript mechanics
  • Senior developers might remove “unused” super(props) parameters, not realizing the props argument is sometimes needed for parent class initialization

Real-World Impact

The consequences include:

  • Component rendering failures – React won’t mount components with malformed constructors
  • Development velocity loss – junior developers blocked on cryptic errors
  • Code review churn – repeated back-and-forth on simple constructor patterns
  • Deployment blockers – CI/CD pipelines fail on linting or runtime errors
  • Inconsistent patterns – mixed usage of super() vs super(props) across codebase

Example or Code

// ❌ WRONG - Missing super()
class MyComponent extends React.Component {
  constructor() {
    this.state = { value: 0 };
  }
  render() { return 
Hello
; }
}

// ❌ WRONG - Using this before super()
class MyComponent extends React.Component {
  constructor() {
    this.state = { value: 0 };
    super();
  }
  render() { return 
Hello
; }
}

// ✅ CORRECT - Basic pattern
class MyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.state = { value: 0 };
  }
  render() { return 
Hello
; }
}

// ✅ CORRECT - super() without arguments also works
class MyComponent extends React.Component {
  constructor(props) {
    super();
    this.state = { value: 0 };
  }
  render() { return 
Hello
; }
}

How Senior Engineers Fix It

Senior engineers address this by:

  • Teaching the JavaScript rule, not just React’s requirement – it’s an ES6 class inheritance law
  • Using super(props) consistently to ensure parent class receives props if needed for internal logic
  • Adding ESLint rules like no-useless-constructor to prevent unnecessary constructors when not needed
  • Refactoring to functional components with hooks to eliminate constructor boilerplate entirely
  • Documenting the pattern in team style guides with clear examples
  • Using code generation templates that include correct constructor patterns

Why Juniors Miss It

Junior developers typically:

  • Don’t understand super() is a JavaScript requirement, not React-specific
  • Think super() is optional because some examples show constructors without it
  • Copy working code but remove “unused” parameters during cleanup
  • Don’t realize that class inheritance has strict ordering rules for initialization
  • Focus on React concepts but miss fundamental JavaScript ES6 class mechanics
  • Receive errors that say “must call super constructor” without understanding the inheritance chain being broken