v8/test/mjsunit/regress/regress-877615.js

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Number.prototype.toLocaleString = function() { return 'invalid'; };
assertEquals('invalid', [1].toLocaleString());  // invalid

Number.prototype.toLocaleString = 'invalid';
assertThrows(function() { [1].toLocaleString(); });  // Not callable.

delete Number.prototype.toLocaleString;
Number.prototype.toString = function() { return 'invalid' };
assertEquals([1].toLocaleString(), 'invalid');  // Uses ToObject on elements.
assertEquals([1].toString(), '1');        // Uses ToString directly on elements.