Skip to main content

Always End "if ... else if" Constructs with an "else" Clause

High
Reliabilitydefensive programming

What is it?​

This practice enforces that every "if" statement followed by one or more "else if" statements must conclude with a final "else" clause. The final "else" either handles unexpected cases or includes a comment explaining why no action is taken.

Why apply it?​

Not providing a final "else" clause can lead to unhandled cases, making the code fragile and hard to maintain. Including a final "else" clause follows a defensive programming approach, similar to requiring a "default" case in switch statements, which improves the overall robustness and readability of your code.

How to Fix it?​

Review all conditional chains that use "if ... else if" statements and ensure that a concluding "else" clause is added. The "else" clause should take appropriate actions (like throwing an error) or contain a comment explaining why no further action is required.

Examples​

Example 1:​

Positive​

Correct implementation following the practice.

function processValue(x: number): void {
  if (x === 0) {
    console.log("x is zero");
  } else if (x === 1) {
    console.log("x is one");
  } else {
    // Defensive programming: unexpected value case handled explicitly.
    throw new Error("Unexpected value for x: " + x);
  }
}

Negative​

Incorrect implementation that violates the practice.

function processValue(x: number): void {
  if (x === 0) {
    console.log("x is zero");
  } else if (x === 1) {
    console.log("x is one");
  }
  // Noncompliant: missing final 'else' to handle unexpected values.
}

Example 2:​

Positive​

Correct implementation following the practice.

interface Order {
  status: string;
}

function handleOrder(order: Order): void {
  if (order.status === "pending") {
    console.log("Order is pending. Preparing for processing.");
  } else if (order.status === "completed") {
    console.log("Order completed successfully.");
  } else if (order.status === "cancelled") {
    console.log("Order has been cancelled.");
  } else {
    // Defensive programming: log a warning if the order status is unrecognized.
    console.warn("Unhandled order status:", order.status);
  }
}

Negative​

Incorrect implementation that violates the practice.

interface Order {
  status: string;
}

function handleOrder(order: Order): void {
  if (order.status === "pending") {
    console.log("Order is pending. Preparing for processing.");
  } else if (order.status === "completed") {
    console.log("Order completed successfully.");
  } else if (order.status === "cancelled") {
    console.log("Order has been cancelled.");
  }
  // Noncompliant: missing final 'else' to handle unrecognized statuses.
}