How to avoid common JavaScript pitfalls and bugs

· Category: JavaScript

Short answer

Common pitfalls include relying on implicit coercion, mutating shared state, misunderstanding this, and creating closure loops with var.

Steps

  1. Always use strict equality: javascript if (x === 5) { /* ... */ }
  2. Declare variables with let or const: javascript for (let i = 0; i < 3; i++) { /* ... */ }
  3. Avoid mutating arguments: javascript function update(obj) { return { ...obj, active: true }; }
  4. Bind or use arrow functions to preserve this.
  5. Await all Promises before using their values.

Tips

  • Use a linter like ESLint with strict rules.
  • Write unit tests for edge cases involving null, undefined, and empty collections.

Common issues

  • typeof null === "object" is a legacy bug; use === null instead.
  • NaN is not equal to itself; use Number.isNaN().
  • Modifying an array while iterating over it skips elements.