JavaScript Break
The Break Statement
The break statement "jumps out" of loops and switches.
The break statement terminates the execution
of a loop or a switch statement.
Break in Loops
When break is encountered in a loop,
the loop terminates immediately.
The program control is transfered to the statements following the loop.
No more loop iterations are executed.
Example
Terminate the loop (break the loop) when the loop counter (i) is 3:
for (let i = 0; i < 10; i++) {
if (i === 3) { break; }
text += "The number is " + i + "<br>";
}
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Note
You have already seen the break statement used in an earlier
chapter of this tutorial.
It was used to "jump out" of a switch statement.
Break in a Switch
In a switch statement, a break statement
will exit the switch block after a matching case is executed. Without break, execution would "fall through" to subsequent case blocks.
Example
Use the weekday number to calculate the weekday name:
switch (new Date().getDay()) {
case 0:
day = "Sunday";
break;
case 1:
day = "Monday";
break;
case 2:
day = "Tuesday";
break;
case 3:
day = "Wednesday";
break;
case 4:
day = "Thursday";
break;
case 5:
day = "Friday";
break;
case 6:
day = "Saturday";
}
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Note
The break keyword is crucial for preventing a switch "fall-through."
Without break, the code will continue to execute the next case blocks
(and the default block if present) even if their values do not match the expression.
JavaScript Labels
A label provides a name for a statement, or a block of statements, allowing statements to be referenced to, for program flow control, particularly in loops.
Syntax
A label is an identifier followed by a colon (:).
labelname: statement;
A label precedes a statement or a block of code.
labelname: {
statements
}
Labeled Break
Syntax
break labelname;
The break statement exits a loop or block
and transfers the control to the labeled statement.
The break statement is particularly useful for breaking out of
inner or outer loops from nested loops.
Example
Break to loop1:
let text = "";
loop1: for (let j = 1; j < 5; j++) {
loop2: for (let i = 1; i < 5; i++) {
if (i === 3) { break loop1; }
text += i;
}
}
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Example
Break to loop2:
let text = "";
loop1: for (let j = 1; j < 5; j++) {
loop2: for (let i = 1; i < 5; i++) {
if (i === 3) { break loop2; }
text += i;
}
}
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Note
break and continue
are the only JavaScript statements that can "jump out of" a code block.
A code block is a block of code between { and }.
Without a label reference, break can only
jump out of a loop or a switch.
With a label reference, break can jump out
of any code block:
Example
Break out of the block after the second car:
const cars = ["BMW", "Volvo", "Saab", "Ford"];
list: {
text += cars[0] + "<br>";
text += cars[1] + "<br>";
break list;
text += cars[2] + "<br>";
text += cars[3] + "<br>";
}
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