JavaScript: The Definitive Guide, Fourth Edition

Name

Arguments.length — the number of arguments passed to a function

Availability

JavaScript 1.1; JScript 2; ECMAScript v1

Synopsis

arguments.length

Description

The length property of the Arguments object specifies the number of arguments passed to the current function. This property is defined only within a function body.

Note that this property specifies the number of arguments actually passed, not the number expected. See Function.length for the number of declared arguments. Note also that this property does not have any of the special behavior of the Array.length property.

Example

// Use an Arguments object to check that correct # of args were passed
function check(args) {
    var actual = args.length;           // The actual number of arguments
    var expected = args.callee.length;  // The expected number of arguments
    if (actual != expected) {           // Throw exception if they don't match
        throw new Error("Wrong number of arguments: expected: " +
                         expected + "; actually passed " + actual);
    }
}
// A function that demonstrates how to use the function above
function f(x, y, z) {
    check(arguments);  // Check for correct number of arguments
    return x + y + z;  // Now do the rest of the function normally
}

See Also

Array.length, Function.length