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Common TypeScript Errors: TS2345, TS2339, TS2304 & How to Fix Them

TypeScript error messages are precise — if you know what each code means, you can fix any error in seconds. This guide covers the six most common error codes with the cause, a broken example, and the correct fix.

TS2345 — Argument Not Assignable to Parameter

Full message: Argument of type 'X' is not assignable to parameter of type 'Y'.

Cause: You are calling a function with a value whose type is not compatible with what the function expects. The types can be completely different, or a union type that is too wide.

Broken code

function greet(name: string) {
  return `Hello, ${name}`;
}

const userId: string | number = getUserId(); // could be number
greet(userId); // TS2345: string | number is not assignable to string

Fixed code

// Fix 1: Narrow before calling
if (typeof userId === "string") {
  greet(userId); // ✓ TypeScript knows it's string here
}

// Fix 2: Convert to string
greet(String(userId)); // ✓

// Fix 3: Widen the parameter
function greet(name: string | number) {
  return `Hello, ${name}`;
}
greet(userId); // ✓

TS2339 — Property Does Not Exist on Type

Full message: Property 'X' does not exist on type 'Y'.

Cause: The type does not declare the property you are trying to access. Common causes are typos, missing fields in an interface, or accessing a property only present on one branch of a union without narrowing.

Broken code

interface User { id: number; name: string; }
const user: User = { id: 1, name: "Alice" };

console.log(user.email); // TS2339: Property 'email' does not exist on type 'User'

// Also fires on union types without narrowing
type Shape = { kind: "circle"; radius: number } | { kind: "square"; side: number };
function area(s: Shape) {
  return s.radius * Math.PI; // TS2339: 'radius' does not exist on type 'Shape'
}

Fixed code

// Fix 1: Add the property to the interface
interface User { id: number; name: string; email?: string; }

// Fix 2: Narrow the union type first
function area(s: Shape) {
  if (s.kind === "circle") {
    return s.radius * Math.PI; // ✓ TypeScript knows it's a circle
  }
  return s.side ** 2;
}

// Fix 3: Use optional chaining for properties that might not exist
const email = (user as { email?: string }).email ?? "none";

TS2304 — Cannot Find Name

Full message: Cannot find name 'X'.

Cause: The identifier is not in scope. Most often caused by a missing import, a missing@types package, or a global not included in the tsconfig lib array.

Broken code

// Missing import
const result = _.groupBy(users, "role"); // TS2304: Cannot find name '_'

// Missing @types package
const el = document.getElementById("app"); // TS2304 if 'DOM' not in tsconfig lib

// Typo
const count = useState(0);
const [n, setN] = useSttate(0); // TS2304: Cannot find name 'useSttate'

Fixed code

// Fix 1: Add the import
import _ from "lodash"; // or: npm install --save-dev @types/lodash

// Fix 2: Add 'DOM' to tsconfig lib
{
  "compilerOptions": {
    "lib": ["ES2020", "DOM"]
  }
}

// Fix 3: Fix the typo
const [n, setN] = useState(0); // ✓

TS2322 — Type Not Assignable (Variable Assignment)

Full message: Type 'X' is not assignable to type 'Y'.

Cause: Similar to TS2345 but on variable assignment rather than function arguments. The value you are assigning is not compatible with the declared variable type.

Broken code

let status: "active" | "inactive" = "active";
status = "pending"; // TS2322: 'pending' is not assignable to '"active" | "inactive"'

let count: number = "five"; // TS2322: string not assignable to number

// Common with React setState
const [user, setUser] = useState<User>({ id: 1, name: "Alice" });
setUser("Alice"); // TS2322: string not assignable to User

Fixed code

// Fix 1: Widen the type to accept the new value
let status: "active" | "inactive" | "pending" = "active";
status = "pending"; // ✓

// Fix 2: Correct the assigned value
let count: number = 5; // ✓

// Fix 3: Pass the correct shape
setUser({ id: 1, name: "Alice" }); // ✓

TS2741 — Missing Required Properties

Full message: Property 'X' is missing in type 'Y' but required in type 'Z'.

Cause: You are creating an object literal that does not include all required properties of the target type.

Broken code

interface User {
  id: number;
  name: string;
  email: string;
}

// TS2741: Property 'email' is missing in type '{ id: number; name: string }'
const user: User = { id: 1, name: "Alice" };

// Also common in React — missing required prop
function Avatar({ name, src }: { name: string; src: string }) {
  return <img src={src} alt={name} />;
}
<Avatar name="Alice" /> // TS2741: 'src' is missing

Fixed code

// Fix 1: Provide all required properties
const user: User = { id: 1, name: "Alice", email: "alice@example.com" }; // ✓

// Fix 2: Make the property optional if it may not always be provided
interface User {
  id: number;
  name: string;
  email?: string; // ✓ now optional
}

// Fix 3: Use Partial for partial construction
function createUser(partial: Partial<User>): User {
  return { id: Date.now(), name: "Unknown", email: "", ...partial };
}

TS2769 — No Overload Matches This Call

Full message: No overload matches this call.

Cause: You called a function that has multiple overload signatures, but your arguments do not satisfy any of them. The error typically lists each overload and why it failed — read those closely.

Broken code

// createElement has overloads for known elements and generic elements
import { createElement } from "react";

// Passing wrong type for known element
createElement("div", { unknownProp: true }); // TS2769: unknownProp is not valid for div

// Common with libraries like Axios
import axios from "axios";
// axios.get expects a string URL as first argument
axios.get(42); // TS2769: number is not assignable to string

Fixed code

// Fix: Read the overload error carefully — use the correct types
createElement("div", { className: "container" }); // ✓ className is valid
axios.get("/api/users"); // ✓ string URL

// When the library types are wrong or incomplete:
// Use a type assertion as a last resort
axios.get(42 as unknown as string); // works but loses type safety — prefer the correct fix

// Or look for the correct overload signature:
// Hover over the function in VS Code to see all overloads

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