Let’s discuss control flow. We’ll be covering three powerful techniques for faster, cleaner, and more maintainable code:

  • Push if statements up to centralize logic
  • Move for loops to the bottom to support batching and optimization
  • Move switch logic outside of hot loops.

We’ll also examine the Big O consequences and how compilers benefit from clean structure.

Move if Statements to the Top

If you’re verifying nulls or guards within a function, ask yourself: should this logic be at the calling site instead?

Bad:

js
interface User {
  email: string;
}

function processUser(user: User | null): void {
  if (!user) return;
  sendEmail(user.email);
}

Good:

js
function processUser(user: User): void {
  sendEmail(user.email);
}

const maybeUser = getUser();
if (maybeUser !== null) {
  processUser(maybeUser);
}

Why?

  • Fewer branches within reusable logic
  • Call site has context to inform behavior
  • Enhances type safety and compiler inference

Big O:

Eliminating inner function branching decreases decisions at run-time from O(n) to O(1) per invocation in performance-critical code paths

Pull Down for Loops

Rather than looping externally, bring iteration into the function to take advantage of batching.

Bad:

js
for (let task of taskList) {
  runTask(task);
}

Good:

js
function runTasks(tasks: Task[]): void {
  for (let task of tasks) {
    runTask(task);
  }
}

runTasks(taskList);

Better:

js
function runTasksOptimized(tasks: Task[]): void {
  // Stage 1: Validate
  for (let task of tasks) validate(task);

  // Stage 2: Execute
  for (let task of tasks) execute(task);

  // Stage 3: Cleanup
  for (let task of tasks) console.log(task);
}

Why?

  • Batch-aware logic minimizes the overhead of calls
  • Facilitates vectorization, caching, and stages of the pipeline

Big O:

O(n) remains O(n) but with less branching = better caching and better CPU efficiency

Combine: if Outside, for Inside

Bad:

js
for (let msg of messages) {
  if (urgent) handleUrgent(msg);
  else handleNormal(msg);
}

Good:

js
if (urgent) {
  for (let msg of messages) handleUrgent(msg);
} else {
  for (let msg of messages) handleNormal(msg);
}

Why?

  • Conditional extracted outside the loop
  • No repeated branching, assists CPU prediction

Big O:

  • Same number of steps overall, but reduced branch misprediction and improved runtime

Loop-Switching: Refactor Your Dispatch

Typical Code:

js
for (let item of items) {
  switch (item.kind) {
    case 'text':
      renderText(item);
      break;
    case 'image':
      renderImage(item);
      break;
  }
}

Improved:

js
const textItems = items.filter(i => i.kind === 'text');
const imageItems = items.filter(i => i.kind === 'image');

for (let t of textItems) renderText(t);
for (let i of imageItems) renderImage(i);

Why?

  • Fewer branches in the inner loop
  • Supports multi-pass or parallel strategies

Big O:

Minor increment (2×O(n)), but enhanced locality and optimizable dispatching

Compile-Time Wins: What Compilers Understand

  • Inner loops without branches allow compilers to employ SIMD and loop unrolling
  • Split loops can be parallelized or pipelined
  • Centralized conditions result in fewer jumps and improved CPU branch prediction

Final Thoughts

These aren’t tricks. These are coding models for what works with the machine, not against it.

  • Organize information more effectively:
  • Shun accidental complexity
  • Improve performance (particularly in hot paths)
  • Make debugging and testing simpler

Push your ifs to the top, bring your fors to the bottom, shift your switch aside—and code to please the compiler.

TL;DR (Too Long? Don’t Refactor):

  • ✅ Move if conditions out of inner logic
  • ✅ Batch your logic within for-friendly functions
  • ✅ Split switch into groups prior to looping

Small changes result in big wins. Now go fix some loops!