while - JavaScript 编辑

The while statement creates a loop that executes a specified statement as long as the test condition evaluates to true. The condition is evaluated before executing the statement.

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Syntax

while (condition)
  statement

condition

An expression evaluated before each pass through the loop. If this condition evaluates to true, statement is executed. When condition evaluates to false, execution continues with the statement after the while loop.

statement

An optional statement that is executed as long as the condition evaluates to true. To execute multiple statements within the loop, use a block statement ({ ... }) to group those statements.

Note: Use the break statement to stop a loop before condition evaluates to true.

Examples

Using while

The following while loop iterates as long as n is less than three.

var n = 0;
var x = 0;

while (n < 3) {
  n++;
  x += n;
}

Each iteration, the loop increments n and adds it to x. Therefore, x and n take on the following values:

• After the first pass: n = 1 and x = 1
• After the second pass: n = 2 and x = 3
• After the third pass: n = 3 and x = 6

After completing the third pass, the condition n < 3 is no longer true, so the loop terminates.

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• do...while
• for