Labeled break and continue in Javascript

Introduction

Labeled break and continue help you control loops more precisely when you have nested loops. They let you jump out of or skip iterations in outer loops easily.

When you have loops inside loops and want to stop or skip the outer loop from inside the inner loop.

When searching for a value in a grid or table and want to stop all loops once found.

When processing nested lists and want to skip certain outer loop steps based on inner loop results.

When you want to avoid complex flags or extra variables to control multiple loops.

Syntax

Javascript

labelName: for (initialization; condition; increment) {
  // loop code
  if (condition) {
    break labelName; // exits the labeled loop
    // continue labelName; // skips to next iteration of labeled loop
  }
}

The label name is an identifier followed by a colon before the loop.

Use break labelName; to exit the labeled loop completely.

Use continue labelName; to skip to the next iteration of the labeled loop.

Examples

This breaks out of both loops when i and j are both 1.

Javascript

outer: for (let i = 0; i < 3; i++) {
  for (let j = 0; j < 3; j++) {
    if (i === 1 && j === 1) {
      break outer;
    }
    console.log(i, j);
  }
}

This skips to the next iteration of the outer loop when j is 1, skipping inner loop steps.

Javascript

outer: for (let i = 0; i < 3; i++) {
  for (let j = 0; j < 3; j++) {
    if (j === 1) {
      continue outer;
    }
    console.log(i, j);
  }
}

Sample Program

This program multiplies i and j in nested loops. When the product is greater than 4, it breaks out of the outer loop completely.

Javascript

outerLoop: for (let i = 1; i <= 3; i++) {
  for (let j = 1; j <= 3; j++) {
    if (i * j > 4) {
      break outerLoop;
    }
    console.log(`i=${i}, j=${j}, product=${i*j}`);
  }
}

Important Notes

Labels must be unique identifiers and placed before loops.

Using labeled break and continue can make code harder to read if overused, so use them only when simpler ways are not enough.

Summary

Labeled break and continue let you control outer loops from inside inner loops.

Use break label; to exit the labeled loop completely.

Use continue label; to skip to the next iteration of the labeled loop.

Practice

1.

What does the break label; statement do in JavaScript?

easy

A. It exits the loop identified by the label immediately.

B. It skips the current iteration of the inner loop only.

C. It restarts the entire program from the beginning.

D. It pauses the loop until a condition is met.

Solution

1. Step 1: Understand labeled break

   The break label; statement exits the loop that has the specified label, not just the innermost loop.

2. Step 2: Compare with normal break

   Normal break exits only the current loop, but labeled break exits the labeled outer loop immediately.

3. Final Answer:

   It exits the loop identified by the label immediately. -> Option A

4. Quick Check:

   break label exits labeled loop [OK]

Hint: Labeled break exits the named loop, not just inner loop [OK]

Common Mistakes:

• Thinking break label only skips current iteration
• Confusing break label with continue label
• Assuming break label pauses the loop

2.

Which of the following is the correct syntax to continue the outer loop labeled outerLoop?

outerLoop: for(let i = 0; i < 3; i++) {
  for(let j = 0; j < 3; j++) {
    // What goes here?
  }
}

easy

A. continue outerLoop;

B. continue (outerLoop);

C. continue: outerLoop;

D. continue to outerLoop;

Solution

1. Step 1: Recall labeled continue syntax

   The correct syntax to continue a labeled loop is continue labelName; without parentheses or extra words.

2. Step 2: Match options with syntax

   continue outerLoop; matches the correct syntax exactly. Options B, C, and D are invalid syntax.

3. Final Answer:

   continue outerLoop; -> Option A

4. Quick Check:

   continue labelName; is correct syntax [OK]

Hint: Use 'continue label;' exactly, no parentheses or colons [OK]

Common Mistakes:

• Adding parentheses around label
• Using colon after continue
• Writing extra words like 'to'

3.

What is the output of the following code?

outer: for(let i = 1; i <= 3; i++) {
  for(let j = 1; j <= 3; j++) {
    if(j === 2) continue outer;
    console.log(i, j);
  }
}

medium

A. 1 1
1 3
2 1
3 1

B. 1 1
2 1
3 1

C. 1 1
1 3
2 1
2 3
3 1
3 3

D. 1 1
2 2
3 3

Solution

1. Step 1: Understand continue outer;

   When j === 2, continue outer; skips to the next iteration of the outer loop, skipping the rest of inner loop and console.log for that i.

2. Step 2: Trace iterations

   For i=1: j=1 logs '1 1', j=2 triggers continue outer (skip to i=2). For i=2: j=1 logs '2 1', j=2 triggers continue outer (skip to i=3). For i=3: j=1 logs '3 1', j=2 triggers continue outer (loop ends after i=3).

3. Final Answer:

   1 1 2 1 3 1 -> Option B

4. Quick Check:

   continue outer skips inner loop rest [OK]

Hint: continue label skips to next outer loop iteration [OK]

Common Mistakes:

• Thinking continue outer skips only inner iteration
• Expecting all inner loop logs
• Confusing break and continue effects

4.

Find the error in this code snippet:

outerLoop: for(let i = 0; i < 2; i++) {
  for(let j = 0; j < 2; j++) {
    if(i === j) break;
    if(j === 1) continue outerLoop;
    console.log(i, j);
  }
}

medium

A. The label name is missing a colon.

B. Using continue outerLoop; inside inner loop is invalid.

C. The break; statement breaks only inner loop, not labeled loop.

D. No error; code runs correctly.

Solution

1. Step 1: Analyze break statement

   The break; without label breaks only the innermost loop, not the labeled outer loop.

2. Step 2: Check labeled continue usage

   The continue outerLoop; is valid and skips to next iteration of the labeled loop.

3. Final Answer:

   The break; statement breaks only inner loop, not labeled loop. -> Option C

4. Quick Check:

   break without label affects inner loop only [OK]

Hint: break without label breaks inner loop only [OK]

Common Mistakes:

• Assuming break breaks labeled loop without label
• Thinking continue outerLoop is invalid
• Confusing label syntax

5.

Given the nested loops below, how can you skip all remaining iterations of the outer loop when j === 3?

outerLoop: for(let i = 1; i <= 5; i++) {
  for(let j = 1; j <= 5; j++) {
    if(j === 3) {
      // What statement here?
    }
    console.log(i, j);
  }
}

hard

A. continue outerLoop;

B. break;

C. continue;

D. break outerLoop;

Solution

1. Step 1: Understand the goal

   We want to stop all remaining iterations of the outer loop when j === 3, meaning exit the outer loop completely.

2. Step 2: Choose correct statement

   break outerLoop; exits the labeled outer loop immediately. Plain break; exits only inner loop. continue; and continue outerLoop; skip iterations but do not exit the outer loop.

3. Final Answer:

   break outerLoop; -> Option D

4. Quick Check:

   break label exits labeled loop [OK]

Hint: Use break label to exit outer loop immediately [OK]

Common Mistakes:

• Using break without label to exit outer loop
• Using continue instead of break
• Confusing continue label with break label