JavaScript — Break

Two loop controllers

break;      // exit the whole loop NOW
continue;   // skip to the next iteration

break

for (let i = 0; i < 10; i++) {
    if (i === 5) break;
    console.log(i);
}
// 0 1 2 3 4 — stops dead at 5

continue

for (let i = 0; i < 5; i++) {
    if (i === 2) continue;
    console.log(i);
}
// 0 1 3 4 — only 2 is skipped

The while-loop trap

continue jumps back BEFORE your increment — infinite loop risk:

let i = 0;
while (i < 5) {
    if (i === 3) continue;   // 😱 i frozen at 3 forever
    console.log(i);
    i++;
}

Fix: increment first, or use for where the step is guaranteed:

for (let i = 0; i < 5; i++) {
    if (i === 3) continue;   // safe — i++ always runs
    console.log(i);
}

Search pattern — stop when found

let found;
for (const user of users) {
    if (user.id === targetId) {
        found = user;
        break;               // don't waste cycles scanning the rest
    }
}

// …though find() expresses this better:
const found2 = users.find(u => u.id === targetId);

Skip invalid data

for (const v of [10, null, 20, null, 30]) {
    if (v === null) continue;
    total += v;
}

Nested loops — nearest exit only

for (const row of grid) {
    for (const cell of row) {
        if (cell === null) break;   // exits INNER loop only
        render(cell);
    }
}

Labeled loops — rare but real

outer:
for (let i = 0; i < 3; i++) {
    for (let j = 0; j < 3; j++) {
        if (i === 1 && j === 1) break outer;     // exits BOTH loops
        if (j === 1) continue outer;             // next OUTER iteration
        console.log(i, j);
    }
}

Readable alternatives usually exist (flags, functions with return, array methods) — reach for labels last.

switch uses break too

Without it, execution falls through into the next case — covered in the switch lesson.

Quick reference

Statement	Effect	Watch out
break	kills current loop entirely	nested → inner only
continue	skips rest of THIS iteration	while-loops can hang
labels	target a specific loop	readability cost

Mini Practice

1. Stop a loop at value 5; log what printed.
2. Skip evens with continue in a for AND fix the while version.
3. Find-first-match with break; rewrite as find().
4. Null-skipping sum over messy data.
5. Nested grid scan exiting both levels with a label.
6. Explain break vs continue in one sentence each.

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