assertEq("abc".includes("a"), true);
assertEq("abc".includes("b"), true);
assertEq("abc".includes("abc"), true);
assertEq("abc".includes("bc"), true);
assertEq("abc".includes("d"), false);
assertEq("abc".includes("abcd"), false);
assertEq("abc".includes("ac"), false);
assertEq("abc".includes("abc", 0), true);
assertEq("abc".includes("bc", 0), true);
assertEq("abc".includes("de", 0), false);
assertEq("abc".includes("bc", 1), true);
assertEq("abc".includes("c", 1), true);
assertEq("abc".includes("a", 1), false);
assertEq("abc".includes("abc", 1), false);
assertEq("abc".includes("c", 2), true);
assertEq("abc".includes("d", 2), false);
assertEq("abc".includes("dcd", 2), false);
assertEq("abc".includes("a", 42), false);
assertEq("abc".includes("a", Infinity), false);
assertEq("abc".includes("ab", -43), true);
assertEq("abc".includes("cd", -42), false);
assertEq("abc".includes("ab", -Infinity), true);
assertEq("abc".includes("cd", -Infinity), false);
assertEq("abc".includes("ab", NaN), true);
assertEq("abc".includes("cd", NaN), false);
var myobj = {toString : () => "abc", includes : String.prototype.includes};
assertEq(myobj.includes("abc"), true);
assertEq(myobj.includes("cd"), false);
var gotStr = false, gotPos = false;
myobj = {toString : (function () {
    assertEq(gotPos, false);
    gotStr = true;
    return "xyz";
}),
includes : String.prototype.includes};
var idx = {valueOf : (function () {
    assertEq(gotStr, true);
    gotPos = true;
    return 42;
})};
myobj.includes("elephant", idx);
assertEq(gotPos, true);
assertEq("xyzzy".includes("zy\0", 2), false);
var dots = Array(10000).join('.');
assertEq(dots.includes("\x01", 10000), false);
assertEq(dots.includes("\0", 10000), false);