Generator and Iterator manipulation

eater.js

/**
 * Eater.js version: 0.3.2
 * Usage examples: 
 * // Even squares of numbers between 1-100
 *   _(_.filter( x => x % 2 === 0, _.map(x => x * x, _.range(1, 100))))
 * // 10 coin flips
 *   _(_.pick([true, false]), 10)
 * // first 100 Fibonacci numbers (assuming already defined generator)
 *   _(_.take(100, fibonacci()))
 * // Consume pseudo-array
 *   _({0: 1, 1: 2, length: 2})
 */
window._ = window.eater = (function(){'use strict';
function eater(it, ...args) {
  if(typeof it === 'function') {
    return eater.func(it, ...args);
  } else if(it[Symbol.iterator]) {
    if(typeof args[0] === 'number'|| args[0] instanceof Number) {
      return [...eater.take(args[0], it)];
    } else {
      return [...it];
    }
  } else if(it.next) {
    return eater.take(it);
  } else if(typeof it.length === 'number') {
    return eater.loop(it);
  } else {
    return eater.fill(it);
  }
}
Object.assign(eater, {
  /* Creators */
  *range(start = Infinity, end = null) {
    if(end == null) {
      [start, end] = [1, start];
    }
    for(let i = start; i <= end; i++) {
      yield i;
    }
  },
  *fill(val) {
    while(true) {
      yield val;
    }
  },
  *func(fn, ...args) {
    while(true) {
      yield fn(...args);
    }
  },
  *loop(it) {
    for(let i = 0; i < it.length; i++) {
      yield it[i];
    }
  },
  *pick(a) {
    while(true) {
      yield a[Math.floor(Math.random() * a.length)];
    }
  },
  *join(...its) {
    for(let it of its) {
      yield* it;
    }
  },
  /* Accessors */
  *take(amt, iter) {
    if(iter == null) {
      iter = amt;
      amt = Infinity;
    }
    let it = iter[Symbol.iterator] ? iter[Symbol.iterator]() : iter
    for(let i = 0, n; i < amt && !((n = it.next()).done); i++) {
      yield n.value;
    }
  },
  each(fun, it) {
    if(it == null) {
      return i => each(fun, i);
    } else {
      return each(fun, it);
    }
  },
  get(it) {
    return it.next().value;
  },
  taker(it) {
    return () => it.next().value;
  },
  /* Manipulators */
  map(fun, it) {
    if(it == null) {
      return i => map(fun, i);
    } else {
      return map(fun, it);
    }
  },
  filter(fun, it) {
    if(it == null) {
      return i => filter(fun, i);
    } else {
      return filter(fun, it);
    }
  },
  combine(fun, ...its) {
    if(its.length === 0) {
      return i => combine(fun, i)
    } else {
      return combine(fun, ...its)
    }
  }
});
function* each(fun, it) {
  for(let i of it) {
    fun(i);
    yield i;
  }
}
function* map(fun, it) {
  for(let i of it) {
    yield fun(i);
  }
}
function* filter(fun, it) {
  for(let i of it) {
      if(fun(i)) {
        yield i;
      }
    }
}
function* combine(fun, ...its) {
  while(true) {
    let results = its.map(i => i.next());
    done = results.every(r => r.done);
    if(done) {
      break;
    } else {
      yield fun(...results.map(r => r.value));
    }
  }
}
return eater;
})();