1.9 KiB
1.9 KiB
| title |
|---|
| Labeled Statement |
Labeled Statement
The Labeled Statement is used with the break and continue statements and serves to identify the statement to which the break and continue statements apply.
Syntax
labelname:
statements
Usage
Without the use of a labeled statement the break statement can only break out of a loop or a switch statement. Using a labeled statement allows break to jump out of any code block.
Example
foo: {
console.log("This prints:");
break foo;
console.log("This will never print.");
}
console.log("Because execution jumps to here!")
/* output
This prints:
Because execution jumps to here! */
When used with a continue statement the labeled statement allows you to skip a loop iteration, the advantage comes from being able to jump out from an inner loop to an outer one when you have nested loop statements. Without the use of a labeled statement you could only jump out of the existing loop iteration to the next iteration of the same loop.
Example
// without labeled statement, when j==i inner loop jumps to next iteration
function test() {
for (var i = 0; i < 3; i++) {
console.log("i=" + i);
for (var j = 0; j < 3; j++) {
if (j === i) {
continue;
}
console.log("j=" + j);
}
}
}
/* output
i=0 (note j=0 is missing)
j=1
j=2
i=1
j=0 (note j=1 is missing)
j=2
i=2
j=0
j=1 (note j=2 is missing)
*/
// using a labeled statement we can jump to the outer (i) loop instead
function test() {
outer: for (var i = 0; i < 3; i++) {
console.log("i=" + i);
for (var j = 0; j < 3; j++) {
if (j === i) {
continue outer;
}
console.log("j=" + j);
}
}
}
/*
i=0 (j only logged when less than i)
i=1
j=0
i=2
j=0
j=1
*/