configurable-length.js

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/* Any copyright is dedicated to the Public Domain.

 * http://creativecommons.org/licenses/publicdomain/ */

// Very simple initial test that the "length" property of a function is

// configurable. More thorough tests follow.

var f = function (a1, a2, a3, a4) {};

assertEq(delete f.length, true);

assertEq(f.hasOwnProperty("length"), false);

assertEq(f.length, 0);  // inherited from Function.prototype.length

assertEq(delete Function.prototype.length, true);

assertEq(f.length, undefined);

// Now for the details.

//

// Many of these tests are poking at the "resolve hook" mechanism SM uses to

// lazily create this property, which is wonky and deserving of some extra

// skepticism.

// We've deleted Function.prototype.length. Check that the resolve hook does

// not resurrect it.

assertEq("length" in Function.prototype, false);

Function.prototype.length = 7;

assertEq(Function.prototype.length, 7);

delete Function.prototype.length;

assertEq(Function.prototype.length, undefined);

// OK, define Function.prototype.length back to its original state per spec, so

// the remaining tests can run in a more typical environment.

Object.defineProperty(Function.prototype, "length", {value: 0, configurable: true});

// Check the property descriptor of a function length property.

var g = function f(a1, a2, a3, a4, a5) {};

var desc = Object.getOwnPropertyDescriptor(g, "length");

assertEq(desc.configurable, true);

assertEq(desc.enumerable, false);

assertEq(desc.writable, false);

assertEq(desc.value, 5);

// After deleting the length property, assigning to f.length fails because

// Function.prototype.length is non-writable. In strict mode it would throw.

delete g.length;

g.length = 12;

assertEq(g.hasOwnProperty("length"), false);

assertEq(g.length, 0);

// After deleting both the length property and Function.prototype.length,

// assigning to f.length creates a new plain old data property.

delete Function.prototype.length;

g.length = 13;

var desc = Object.getOwnPropertyDescriptor(g, "length");

assertEq(desc.configurable, true);

assertEq(desc.enumerable, true);

assertEq(desc.writable, true);

assertEq(desc.value, 13);

// Deleting the .length of one instance of a FunctionDeclaration does not

// affect other instances.

function mkfun() {

    function fun(a1, a2, a3, a4, a5) {}

    return fun;

g = mkfun();

var h = mkfun();

delete h.length;

assertEq(g.length, 5);

assertEq(mkfun().length, 5);

// Object.defineProperty on a brand-new function is sufficient to cause the

// LENGTH_RESOLVED flag to be set.

g = mkfun();

Object.defineProperty(g, "length", {value: 0});

assertEq(delete g.length, true);

assertEq(g.hasOwnProperty("length"), false);

// Object.defineProperty on a brand-new function correctly merges new

// attributes with the builtin ones.

g = mkfun();

Object.defineProperty(g, "length", { value: 42 });

desc = Object.getOwnPropertyDescriptor(g, "length");

assertEq(desc.configurable, true);

assertEq(desc.enumerable, false);

assertEq(desc.writable, false);

assertEq(desc.value, 42);

reportCompare(0, 0, 'ok');