Assignment to constant variable

What is Assignment to constant variable?

This TypeError is thrown when you attempt to change the reference of a variable declared with the const keyword. Const declarations create read-only references to values. You cannot reassign them (e.g. const x = 5; x = 6;). Note that for objects declared with const, you can still modify their properties (like const obj = {}; obj.name = 'John'), but you cannot reassign the object itself.

Common Causes

• Reassigning const variables in loops (e.g. inside for loops).
• Accidentally reusing variable names declared with const.
• Typing reassignment operators (=) instead of comparison operators (===) on const variables.

Common Mistakes

• Assuming const variables protect object keys from modification (objects fields can always be modified; only the primary variable reference is constant).

How to Fix

Framework-Specific Examples

try {
  // Throws error on first loop increment
  for (const i = 0; i < 5; i++) {
    console.log(i);
  }
} catch (err) {
  console.error(err.message); // Assignment to constant variable.
}

Server Configuration Examples

# Handled at code level

Best Practices

• Use let by default if you expect variables to change their values.
• Use Object.freeze(obj) to make object structures completely immutable.

Frequently Asked Questions (FAQ)