unscopables-delete.js

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// If obj[@@unscopables][id], then `delete id` works across `with (obj)` scope.

this.niche = 7;

let obj = { niche: 8, [Symbol.unscopables]: { niche: true } };

with (obj) {

    delete niche;

assertEq(obj.niche, 8);

assertEq("niche" in this, false);

// Same thing, but delete a variable introduced by sloppy direct eval.

this.niche = 9;

function f() {

    eval("var niche = 10;");

    with (obj) {

        assertEq(niche, 10);

        delete niche;

    assertEq(niche, 9);

// Of course none of this affects a qualified delete.

assertEq(delete this.niche, true);

assertEq("niche" in this, false);

reportCompare(0, 0);