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LibJS: Implement Iterator.prototype.reduce

This commit is contained in:
Timothy Flynn 2023-06-25 13:41:01 -04:00 committed by Andreas Kling
parent ad42b4ea67
commit acc05480e8
3 changed files with 196 additions and 0 deletions

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describe("errors", () => {
test("called with non-callable object", () => {
expect(() => {
Iterator.prototype.reduce(Symbol.hasInstance);
}).toThrowWithMessage(TypeError, "reducer is not a function");
});
test("iterator's next method throws", () => {
function TestError() {}
class TestIterator extends Iterator {
next() {
throw new TestError();
}
}
expect(() => {
new TestIterator().reduce(() => 0);
}).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(() => {
new TestIterator().reduce(() => 0);
}).toThrow(TestError);
});
test("reducer function throws", () => {
function TestError() {}
class TestIterator extends Iterator {
next() {
return {
done: false,
value: 1,
};
}
}
expect(() => {
new TestIterator().reduce(() => {
throw new TestError();
});
}).toThrow(TestError);
});
test("no available initial value", () => {
function* generator() {}
expect(() => {
generator().reduce(() => 0);
}).toThrowWithMessage(TypeError, "Reduce of empty array with no initial value");
});
});
describe("normal behavior", () => {
test("length is 1", () => {
expect(Iterator.prototype.reduce).toHaveLength(1);
});
test("reducer function sees every value", () => {
function* generator() {
yield "a";
yield "b";
}
let count = 0;
generator().reduce((accumulator, value, index) => {
++count;
switch (index) {
case 0:
expect(value).toBe("a");
break;
case 1:
expect(value).toBe("b");
break;
default:
expect().fail(`Unexpected reducer invocation: value=${value} index=${index}`);
break;
}
return value;
}, "");
expect(count).toBe(2);
});
test("reducer uses first value as initial value", () => {
function* generator() {
yield 1;
yield 2;
yield 3;
}
const result = generator().reduce((accumulator, value) => accumulator + value);
expect(result).toBe(6);
});
test("reducer uses provided value as initial value", () => {
function* generator() {
yield 1;
yield 2;
yield 3;
}
const result = generator().reduce((accumulator, value) => accumulator + value, 10);
expect(result).toBe(16);
});
});