Generator and Iterator manipulation

eater.js

/**
 * Usage: _(_.filter(_.map(_.range(1, 10), x => x * x), x => x % 2 === 0)) // Even squares of numbers between 1-100
 */
window._ = window.eater = (function(){'use strict';
function eater(it) {
  if(typeof it !== 'function' && typeof it.length === 'number') {
    return eater.loop(it);
  } else {
    return [...it];
  }
};
Object.assign(eater, {
  /* Creators */
  *range(start, end) {
    if(end == null) {
      [start, end] = [0, start];
    }
    for(var i = start; i <= end; i++) {
      yield i;
    }
  },
  *fill(val) {
    while(true) {
      yield val;
    }
  },
  *loop(it) {
    for(var i = 0; i < it.length; i++) {
      yield it[i]
    }
  },
  *concat(...its) {
    for(var it of its) {
      yield* it
    }
  },
  /* Accessors */
  *take(iter, amt) {
    var it = iter[Symbol.iterator]()
    for(var i = 0, n; i < amt && !((n = it.next()).done); i++) {
      yield n.value
    }
  },
  /* Manipulators */
  *map(it, fun) {
    for(var i of it) {
      yield fun(i);
    }
  },
  *filter(it, fun) {
    for(var i of it) {
      if(fun(i)) {
        yield i;
      }
    }
  }
});
return eater
})();