586f10b6e1
This is used by discord.com and allowed by the specification: https://tc39.es/ecma262/#sec-relational-operators-runtime-semantics-evaluation
34 lines
1 KiB
JavaScript
34 lines
1 KiB
JavaScript
test("in operator with objects", () => {
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const sym = Symbol();
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const o = { foo: "bar", bar: undefined, [sym]: "qux" };
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expect("" in o).toBeFalse();
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expect("foo" in o).toBeTrue();
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expect("bar" in o).toBeTrue();
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expect("baz" in o).toBeFalse();
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expect("toString" in o).toBeTrue();
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expect(sym in o).toBeTrue();
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});
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test("in operator with arrays", () => {
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const a = ["hello", "friends"];
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expect(0 in a).toBeTrue();
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expect(1 in a).toBeTrue();
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expect(2 in a).toBeFalse();
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expect("0" in a).toBeTrue();
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expect("hello" in a).toBeFalse();
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expect("friends" in a).toBeFalse();
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expect("length" in a).toBeTrue();
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});
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test("in operator with string object", () => {
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const s = new String("foo");
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expect("length" in s).toBeTrue();
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});
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test("error when used with primitives", () => {
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["foo", 123, null, undefined].forEach(value => {
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expect(() => {
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"prop" in value;
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}).toThrowWithMessage(TypeError, "'in' operator must be used on an object");
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});
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});
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