do  statementwhile (condition);

statement

A statement that is executed at least once and re-executed as long as the condition evaluates to true. You can use ablock statement to execute multiple statements.

condition

An expression evaluatedafter each pass through the loop. If this conditionevaluates to true,statement is re-executed. When conditionevaluates to false, execution continues with the statement after thedo...while loop.

Like other looping statements, you can usecontrol flow statements insidestatement:

• break stopsstatement execution and goes to the first statement after the loop.
• continue stopsstatement execution and re-evaluatescondition.

Thedo...while statement syntax requires a semicolon at the end, but theautomatic semicolon insertion process may insert one for you if the lack of a semicolon results in invalid syntax.

In the following example, thedo...while loop iterates at least once andreiterates untili is no longer less than 5.

let result = "";let i = 0;do {  i += 1;  result += `${i} `;} while (i > 0 && i < 5);// Despite i === 0 this will still loop as it starts off without the testconsole.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 usebreak 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 alabeled block statement withbreak:

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:

do {  // …} while ((match = regexp.exec(str)));

But when you do, there are readability tradeoffs. Thewhile documentation has aUsing an assignment as a condition section with our recommendations.

• while
• for
• break
• continue