Generatorの拡張

ex-generator.js

const iter = (function(){
    // 元のGenerator.prototype
    const GeneratorProto = ({*g(){}}).g().constructor.prototype;
    // 拡張してmap,filterを付与したprototype
    const ExtendedGeneratorProto = Object.setPrototypeOf({
        map (func, thisArg = null) {
            const iterable = this;
            return Object.setPrototypeOf(function*() {
                var i = 0;
                for (const item of iterable) {
                    // console.log("iterMap", item, i);
                    yield func.call(thisArg, item, i);
                    i++;
                }
            }(), ExtendedGeneratorProto);
        },
        filter (func, thisArg = null) {
            const iterable = this;
            return Object.setPrototypeOf(function*(){
                var i = 0;
                for (const item of iterable) {
                    // console.log("iterFilter", item, i);
                    if (func.call(thisArg, item, i)) yield item;
                    i++;
                }
            }(), ExtendedGeneratorProto);
        },
        uniq(){
            const iterable = this;
            return Object.setPrototypeOf(function*(){
                var s = new Set();
                for (const item of iterable) {
                    if (!s.has(item)) {
                        yield item;
                        s.add(item);
                    }
                }
            }(), ExtendedGeneratorProto);
        },
        flat() {
            const iterable = this;
            return Object.setPrototypeOf(function*(){
                for (const item of iterable) {
                    if (typeof item === "string") yield item;
                    else if (Symbol.iterator in item) yield* item;
                    else yield item;
                }
            }(), ExtendedGeneratorProto);
        }
    }, GeneratorProto);

    return iterable => {
        return Object.setPrototypeOf(function*() {
            yield* iterable;
        }(), ExtendedGeneratorProto);
    };
}());


// Sample

function* range(start, end, step = 1) {
    for (var i = start; i <= end; i+=step) {
      yield i;
    }
}

[...iter(range(1, 5)).filter(i => i%2 == 1).map(i => i ** i)]
// => [1, 27, 3125]