statement
A statement that is executed at least once and re-executed as long as the condition evaluates to true. You can use a
block statement
to execute multiple statements.
condition
An expression evaluated
after
each pass through the loop. If this condition
evaluates to true
,
statement
is re-executed. When condition
evaluates to false
, execution continues with the statement after the
do...while
loop.
Like other looping statements, you can use
control flow statements
inside
statement
:
break
stops
statement
execution and goes to the first statement after the loop.
continue
stops
statement
execution and re-evaluates
condition
.
The
do...while
statement syntax requires a semicolon at the end, but the
automatic semicolon insertion
process may insert one for you if the lack of a semicolon results in invalid syntax.
In the following example, the
do...while
loop iterates at least once and
reiterates until
i
is no longer less than 5.
let result = "";
let i = 0;
i += 1;
result += `${i} `;
} while (i > 0 && i < 5);
// Despite i === 0 this will still loop as it starts off without the test
console.log(result);
Because the statement is always executed once, do...while (false) is the same as executing the statement itself. This is a common idiom in C-like languages, which allows you to use break to break out of branching logic early.
do {
if (!user.loggedIn) {
console.log("You are not logged in");
break;
const friends = user.getFriends();
if (!friends.length) {
console.log("No friends found");
break;
for (const friend of friends) {
handleFriend(friend);
} while (false);
// The rest of code
In JavaScript, there are some alternatives, such as using a labeled block statement with break:
handleFriends: {
if (!user.loggedIn) {
console.log("You are not logged in");
break handleFriends;
const friends = user.getFriends();
if (!friends.length) {
console.log("No friends found");
break handleFriends;
for (const friend of friends) {
handleFriend(friend);
Or using a function:
function handleFriends() {
if (!user.loggedIn) {
console.log("You are not logged in");
return;
const friends = user.getFriends();
if (!friends.length) {
console.log("No friends found");
return;
for (const friend of friends) {
handleFriend(friend);
In some cases, it can make sense to use an assignment as a condition, such as this:
