alert (alert (1)) - displays undefined alert (alert (1) && alert (2));

  • You should not ask a new question by changing the text of the question fifteen hours after its publication. - Igor
  • learn.javascript.ru/logical-ops - Duck Learns to Hide
  • The modified version was not preserved right away - Elvis

3 answers 3

Thinking is great, but sometimes easier to read:

https://www.w3schools.com/jsref/met_win_alert.asp

Window alert () Method

Return Value: No return value

(Returns: Returns nothing)

Does not return:

var test = alert(1); console.log(test);

Returns:

 var test = confirm("Are you sure?"); console.log(test);

Returns:

 function multiply(a, b) { return a * b; } console.log(multiply(2, 3));

Does not return:

 function multiplyAndShow(a, b) { var c = a * b; document.getElementById("result").innerText = c; } console.log(multiplyAndShow(2, 3)); 
 <span id="result">empty</span>

  • when alert (1) is displayed 1 - is this a return? I think because of this I get confused - Elvis
  • @Elvis alert displays 1 , because this is what alert does — it shows a window with a string representation of what is passed to it as a parameter. It has nothing to do with the value returned by the alert function. - Igor
  • Can you please provide an example of a function that returns a value? - Elvis
  • @Elvis added an example in response - Igor
  • Thank you very much! Did I understand correctly that something is returning - these are functions, where I have to answer or enter something? That is, there is usually not a single action - Elvis

will print first 1 (internal alert), and then undefined (what the internal alert returned), and at the end will remain undefined (what the external alert returns)

  • I do not fully understand. Above wrote that returns nothing, but you write in 2 brackets that he returned an internal alert: ( - Elvis
  • @Elvis in terms of javascript-a - “returns nothing” is the same as “returns undefined ” - Igor

The alert() function returns no value . It means that

 alert(1)

It is not a convenient parameter for any function, including the alert() :

 alert(alert(1)) // alert(1) ошибочный параметр для alert()
  • What does an error parameter mean? - Grundy