break
The break
statement terminates the current loop,
switch
, or label
statement and transfers program control to the statement following the terminated
statement.
Syntax
break [label];
label
Optional-
Identifier associated with the label of the statement. If the statement is not a loop or
switch
, this is required.
Description
The break
statement includes an optional label that allows the program to
break out of a labeled statement. The break
statement needs to be nested
within the referenced label. The labeled statement can be any
block statement; it does not have to be
preceded by a loop statement.
A break
statement, with or without a following label, cannot be used
within the body of a function that is itself nested within the current loop, switch, or
label statement that the break
statement is intended to break out of.
Examples
break in while loop
The following function has a break
statement that terminates the
while
loop when i
is 3, and then returns
the value 3 * x
.
function testBreak(x) {
var i = 0;
while (i < 6) {
if (i == 3) {
break;
}
i += 1;
}
return i * x;
}
break in switch statements
The following code has a break
statement that terminates the
switch
statement when a case is matched and the
corresponding code has ran
const food = "sushi";
switch (food) {
case "sushi":
console.log("Sushi is originally from Japan.");
break;
case "pizza":
console.log("Pizza is originally from Italy.");
break;
default:
console.log("I have never heard of that dish.");
break;
}
break in labeled blocks
The following code uses break
statements with labeled blocks. A
break
statement must be nested within any label it references. Notice that
inner_block
is nested within outer_block
.
outer_block: {
inner_block: {
console.log('1');
break outer_block; // breaks out of both inner_block and outer_block
console.log(':-('); // skipped
}
console.log('2'); // skipped
}
break in labeled blocks that throw
The following code also uses break
statements with labeled blocks, but
generates a SyntaxError
because its break
statement is within
block_1
but references block_2
. A break
statement
must always be nested within any label it references.
block_1: {
console.log('1');
break block_2; // SyntaxError: label not found
}
block_2: {
console.log('2');
}
break within functions
SyntaxError
s are also generated in the following code examples which use
break
statements within functions that are nested within a loop, or labeled
block that the break
statements are intended to break out of.
function testBreak(x) {
var i = 0;
while (i < 6) {
if (i == 3) {
(function() {
break;
})();
}
i += 1;
}
return i * x;
}
testBreak(1); // SyntaxError: Illegal break statement
block_1: {
console.log('1');
( function() {
break block_1; // SyntaxError: Undefined label 'block_1'
})();
}
Specifications
Specification |
---|
ECMAScript Language Specification # sec-break-statement |
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