concat-spreadable-primitive.js

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/* Any copyright is dedicated to the Public Domain.

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

"use strict";

// Primitive values should never be tried to spread

let primitives = [

10,

    false,

    Symbol()

    // Can't change String.prototype.length

];

for (let value of primitives) {

    let prototype = Object.getPrototypeOf(value);

    prototype[Symbol.isConcatSpreadable] = true;

    Object.defineProperty(prototype, "length", {

        configurable: true,

        get() {

            // Should never invoke length getter

            assertEq(true, false);

},

});

    let x = [1, 2].concat(value);

    assertDeepEq(x, [1, 2, value]);

    delete prototype[Symbol.isConcatSpreadable];

    delete prototype.length;

    prototype.length;

reportCompare(true, true);