Yield - Generator Functions (node.js)

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Do you know how to use generator functions in  javascript? So this is the topic of this video We are going to see how to define a generator  function using this syntax and what is its propose a function that can stop and return a value in  the middle of its execution and in a next moment continuing the execution until finding another  stopping point that will be this "yield" keyword and it will repeat until the function ends  or find a return value or an exception is triggering. So lets experiment this functionality  together. Here in the upper part of this code we have a generator function defined. Whats the  difference between a generator function and a normal function? It is because it has this star  at the side of the function keyword and inside its body, once its defined as a generator function,  it can have the yield keyword, it could have more than one yield keyword, if you have more than one  point of return. The idea is that the function will start to run and it will stop the running of  the workflow of the function as soon as it finds a yield keyword, then the value at the right of  the yield keyword will be returned for who has called the function. So here the function is just  created and now with the next statement we take the next value its find, it means until  the next yield keyword is found then it returns this value once its returning we can  read the value and its blocked the function simply stop to execute. Then in the next time we  call the next again it will run the line below and it will keep running until  it finds one the yield keyword, it finds that, then the value could be returned and its again stop  it and then if we call the next value but it do not find the yield keyword but finds the end of the  function, what happens? It will ends in this case the undefined value will be returned, because  when the function ends without the return keyword it returns undefined. It its the same this  function the way it is its the same as do that the same as do that, okay? So having an undefined  return or no return is the same. So in this example here it will be returned undefined because it  will end the execution, otherwise if you want to return a different value we just can return  here something different like a zero, okay ? Lets try that together. Lets execute  this function that will be created with this constructor, this seed, like  zero, so we are going to execute that and okay, so here first execution its start with  zero execute until arrives in the yield keyword and return the on value that that has entered zero.  Then we call the next again and what happens? Index was incremented by one its twwo less than  two and then stop in the next yield and return the one there and then we call again the next  value what happened it was increased by 2 2 but when arrives here in the yield 2 is not  smaller than 2 then it jumps to out and it was not returning the number two, it was returned then undefined , because theres no return statement. If we want to return the index value  anyway we could for instance just return here the index variable and now instead of undefined.  Lets see what we are going to receive we clear that, we execute that again, and you see now  it returns two, why? Because it really has  incremented by one after the one so it reads  the value two it jumps the while statement because now it does not match the condition  but it really was two and then return the latest value of the variable and the function ends  and the generator is over, okay? So this was one overview about how to use the generator functions.  Remember of these key aspects: the star at the side of the function name; the yield keyword; the next method; and the value property. With these concepts you are able to create your own generated  functions. You can download this source code we have demonstrated by the link available below  in the video description. Thank you for watching!!!