Skip to the next outer-loop iteration
Nested iteration
JS Puzzles · Const
Label Statements
A label names a loop so nested break or continue can target that loop. It provides structured control flow, not an arbitrary jump mechanism.
How it works
A label gives a statement an identifier followed by a colon. A break or continue nested inside that labeled statement can refer to the identifier: break exits the labeled statement, while continue advances a labeled loop. Labels are not general-purpose jumps.
Syntax
labelName: statementKey points
- The usual form places an identifier and colon before a loop, such as outer: for (...).
- A labeled continue skips the remainder of the current iteration and continues with the next iteration of the named loop.
- When continue names a label, control advances in that labeled loop rather than necessarily the innermost loop.
- The labeled statement syntax is labelName: followed by a loop statement.
Common mistakes
- A label cannot directly prefix a declaration such as const; wrap the declaration in a block if needed.
Example: Continue an outer loop
outer: for (const row of [[1, 2], [3, 4]]) {
for (const value of row) {
if (value === 3) continue outer;
console.log(value);
}
}The labeled continue skips the rest of the inner loop and starts the next iteration of the outer loop.
When to use it
Exit a named outer loop early
Nested iteration
Interview questions
QWhat is a labeled statement?
A label is an identifier followed by a colon that prefixes a statement. A nested break can exit that labeled statement, and a nested continue can move to the next iteration when the labeled statement is a loop.
Follow-up: Can a labeled break target a non-loop statement? Yes. For example, a labeled block can be exited with break, but continue requires a labeled loop.
QWhat restrictions apply to break and continue with labels?
The label must contain the break or continue statement lexically. A break label exits the labeled statement and resumes after it; continue label proceeds with the next iteration of the labeled loop.
Follow-up: What happens if the label is outside the statement containing the jump? The program is invalid because the referenced label is not in the required containing statement.
QAre labels equivalent to goto?
JavaScript labels do not provide arbitrary control flow. They work only with break and continue, so they cannot jump into an unrelated location in the program.
Follow-up: Can a label be attached directly to a const declaration? No; labels apply to statements, so place the declaration inside a block statement.
Related
breakcontinueforwhile