The break keyword is a 'jump' statement. It is used in an loop to abort the current cycle and exit from the smallest enclosing loop immediately. Execution continues at the line following the statement block associated with the loop.
A break statement can only legally exist inside a while or for loop in an ECMA-compliant implementation. Implementations that provide additional iterator types may also honor the same behavior for the break statement.
ECMA 262 edition 2 - section - 10.1.4
ECMA 262 edition 2 - section - 12.8
ECMA 262 edition 3 - section - 10.1.4
ECMA 262 edition 3 - section - 12.8