learn-generators

1-run.js

//Exercise 1
/*Write a range generator-function that takes from and to arguments.
Print the numbers as strings within the specified range, one per line.
Follow this boilerplate:
*/
    function *range(from, to) {
      // your code goes here
      for(var i = from; i <= to; i++) {
        yield i;
      }
    }
    for (var r of range(5, 10)) {
        console.log( r );
    }
    // should print: 5, 6, 7, 8, 9, 10
 

2-factorial.js

//Exercise 2
/*fWrite a generator function factorial that, given an input number, starts at 1 and goes
up to the number, yielding the factorial of each number along the way.
Don't use recursion. Use a loop.
Follow this boilerplate:
*/
function *factorial (n) {
    var result = 1;
    for (var i = 1; i <= n; i++) {
      result *= i;
      yield result;
    }
  }

  for (var n of factorial(5)) {
    console.log(n)
  }

3-delegating.js

//Exercise 3
/*Task
Write generator-function flat that takes nested array inside and flattens it.
Follow this boilerplate:
*/
function *flat (arr) {
    if (Array.isArray(arr)) {
      for (var i = 0; i < arr.length; i++) {
        yield* flat(arr[i]);
      }
    } else {
      yield arr;
    }
  }

  var A = [1, [2, [3, 4], 5], 6];
  for (var f of flat(A)) {
      console.log( f );
  }
  // 1 2 3 4 5 6

4-error.js

//Exercise 4
/*Write a generator-function upper that takes an array of strings and
yields each of them in upper case.
The problem: some person sent a number into the upper and it's broken.
Please fix it. If upper gets a number it should return null.
Follow this boilerplate
*/
function* upper(items) {
    // your code goes here
    for (let item of items) {
        try {
            yield item.toUpperCase()
        } catch (e) {
            yield null
        }
    }
}

var bad_items = ['a', 'B', 1, 'c'];

for (var item of upper(bad_items)) {
    console.log(item);
}
// want to log: A, B, null, C
 

5-async.js

//Exercise 5
/*Add error handling to this boilerplate. Teach run to throw an exception and
catch that in generator. firstFile should be null if it doesn't exist.
Follow this boilerplate:
*/
var fs = require("fs");

function run(generator) {
    var it = generator(go)

    function go(err, result) {
        if (err) return it.throw(null)
        it.next(result)
    }
    go()
    // improve `run` above
}

run(function* (done) {
    // catch exception
    try {
        var dirFiles = yield fs.readdir("NoNoNoNo", done); // No such dir
    } catch (e) {
        console.log(e)
    }

    var firstFile = dirFiles[0]; // TypeError: Cannot read property '0' of undefined
    console.log(firstFile);
});

6-promise.js

//Exercise 6
/*
Write run function that gets a generator as an argument, starts it and
yields promise value foo. Use run from callback exercise as a example.

Follow this boilerplate:
*/
function getFoo () {
    return new Promise(function (resolve, reject){
      resolve('foo');
    });
  }

  function run (generator) {
    var it = generator();

    function go(result) {
      // take a look also on `Generator.prototype.return`
      if (result.done) return result.value;

      return result.value.then(function (value) {
        return go(it.next(value));
      }, function (error) {
        return go(it.throw(error));
      });

    }

    go(it.next());
  }

  run(function* () {
    try {
      var foo = yield getFoo();
      console.log(foo);
    } catch (e) {
      console.log(e);
    }
  });