configurable-length-builtins.js

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/* Any copyright is dedicated to the Public Domain.

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

// Deleting .length from a variety of builtin functions works as expected.

for (var fun of [Math.sin, Array.prototype.map, eval]) {

    assertEq(delete fun.length, true);

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

    assertEq("length" in fun, true);  // still inheriting Function.prototype.length

    assertEq(fun.length, 0);

    // The inherited property is nonwritable, so assigning still fails

    // (silently, in sloppy mode).

    fun.length = Math.hypot;

    assertEq(fun.length, 0);

    // It can be shadowed via defineProperty.

    Object.defineProperty(fun, "length", {value: Math.hypot});

    assertEq(fun.length, Math.hypot);

reportCompare(0, 0, 'ok');