ForStatement

ForStatement is a looping construct used to repeat a block of code a controlled number of times. In many languages it is represented in the language grammar as a for loop with an initializer, a loop condition, and an update expression executed after each iteration. In the ECMAScript specification, ForStatement corresponds to the standard for loop syntax: for (init; test; update) statement.

Syntax and components: init initializes the loop variable (it can be a variable declaration or an expression statement), test is a boolean expression evaluated before each iteration, and update is an expression evaluated after each iteration. Any of init, test, or update may be omitted, giving forms such as for (; test; ) and for (;;).

Semantics: The loop begins by evaluating init once. If test is present and evaluates to true, the body executes; after the body, update is evaluated, then test is evaluated again. When test evaluates to false, the loop terminates. The loop body can contain break or continue statements to alter control flow.

Variants: ForStatement is distinct from ForInStatement and ForOfStatement in JavaScript, which iterate over object property names or values respectively. In other languages, for loops may differ in how scoping and update semantics work; some languages require the initializer to declare a loop counter, others reuse existing variables.

Examples: for (let i = 0; i < 10; i++) { … } and for (var i = 0; i < n; i += 2) { … }.

See also: While loop, Do-While loop, ForInStatement, ForOfStatement.