JS Break

JavaScript break & continue: Flow Control & Labeled Statements

The break statement immediately terminates the current loop or switch block. The continue statement skips the remainder of the current iteration and jumps directly to the next loop evaluation. Labels allow control statements to target specific outer nested loops.

break vs continue Execution Path

flowchart TD
    Loop["Loop Iteration"] --> CheckItem{"Inspect Item"}
    CheckItem -- "continue hit" --> Skip["Skip remaining body -> Next Iteration"]
    CheckItem -- "break hit" --> Exit["Terminate Loop Entirely"]
    CheckItem -- "Normal" --> Exec["Execute remaining body"]

Flow Control Keyword Summary

Practical Code Example

// Demonstrating break, continue, and labeled loops

// 1. continue: Skipping odd numbers
console.log("--- Filter Even Numbers with continue ---");
for (let i = 1; i <= 5; i++) {
  if (i % 2 !== 0) {
    continue; // Skip rest of loop body for odd numbers
  }
  console.log(`Even Number: ${i}`);
}

// 2. break: Short-circuit search
console.log("
--- Early Exit Search with break ---");
const items = ["Apple", "TargetItem", "Banana", "Cherry"];
for (const item of items) {
  if (item === "TargetItem") {
    console.log(`Found target item '${item}'! Exiting loop.`);
    break; // Terminate loop early
  }
}

// 3. Labeled Outer Loop Exit
console.log("
--- Labeled Multi-level Loop Exit ---");
outerMatrixLoop: for (let r = 0; r < 3; r++) {
  for (let c = 0; c < 3; c++) {
    if (r === 1 && c === 1) {
      console.log(`Target found at matrix cell [${r}][${c}]. Exiting outer matrix loop!`);
      break outerMatrixLoop; // Exits outer loop directly!
    }
    console.log(`Processing Cell [${r}][${c}]`);
  }
}

Best Practices & Gotchas

• Use break for Search Short-Circuiting: Once a search target is located in a loop, invoke break to save CPU cycles.
• Use Labels Sparingly: Labeled loops increase code complexity. If nested loops require labeled breaks, consider refactoring the inner loop into a separate helper function with return.
• continue in while Loops: Be careful when placing continue inside while loops; ensure the counter increment happens BEFORE the continue statement to avoid infinite loops.

Self-Check Challenge

What happens if continue is executed in a while loop BEFORE the counter increment line i++?