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LibJS: Implement Iterator.prototype.filter

This commit is contained in:
Timothy Flynn 2023-06-25 10:05:36 -04:00 committed by Andreas Kling
parent 3eb2e4e08a
commit deeee65e37
3 changed files with 224 additions and 0 deletions

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describe("errors", () => {
test("called with non-callable object", () => {
expect(() => {
Iterator.prototype.filter(Symbol.hasInstance);
}).toThrowWithMessage(TypeError, "predicate is not a function");
});
test("iterator's next method throws", () => {
function TestError() {}
class TestIterator extends Iterator {
next() {
throw new TestError();
}
}
expect(() => {
const iterator = new TestIterator().filter(() => true);
iterator.next();
}).toThrow(TestError);
});
test("value returned by iterator's next method throws", () => {
function TestError() {}
class TestIterator extends Iterator {
next() {
return {
done: false,
get value() {
throw new TestError();
},
};
}
}
expect(() => {
const iterator = new TestIterator().filter(() => true);
iterator.next();
}).toThrow(TestError);
});
test("predicate function throws", () => {
function TestError() {}
class TestIterator extends Iterator {
next() {
return {
done: false,
value: 1,
};
}
}
expect(() => {
const iterator = new TestIterator().filter(() => {
throw new TestError();
});
iterator.next();
}).toThrow(TestError);
});
});
describe("normal behavior", () => {
test("length is 1", () => {
expect(Iterator.prototype.filter).toHaveLength(1);
});
test("predicate function sees every value", () => {
function* generator() {
yield "a";
yield "b";
}
let count = 0;
const iterator = generator().filter((value, index) => {
++count;
switch (index) {
case 0:
expect(value).toBe("a");
break;
case 1:
expect(value).toBe("b");
break;
default:
expect().fail(`Unexpected predicate invocation: value=${value} index=${index}`);
break;
}
return true;
});
for (const i of iterator) {
}
expect(count).toBe(2);
});
test("predicate function can select values", () => {
function* generator() {
yield 1;
yield 0;
yield 2;
yield 0;
}
const iterator = generator().filter(value => value > 0);
let value = iterator.next();
expect(value.value).toBe(1);
expect(value.done).toBeFalse();
value = iterator.next();
expect(value.value).toBe(2);
expect(value.done).toBeFalse();
value = iterator.next();
expect(value.value).toBeUndefined();
expect(value.done).toBeTrue();
});
test("predicates can be chained", () => {
function* generator() {
yield 1;
yield 0;
yield 2;
yield 0;
}
let firstFilterCount = 0;
let secondFilterCount = 0;
const iterator = generator()
.filter(value => {
++firstFilterCount;
return value > 0;
})
.filter(value => {
++secondFilterCount;
return value > 1;
});
let value = iterator.next();
expect(value.value).toBe(2);
expect(value.done).toBeFalse();
value = iterator.next();
expect(value.value).toBeUndefined();
expect(value.done).toBeTrue();
expect(firstFilterCount).toBe(4);
expect(secondFilterCount).toBe(2);
});
});