javascript - Prompt user for specific input, loop and prompt until correct input is entered - Stack Overflow

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I am new here and currently learning JavaScript. In the code below, how can I get it to loop and still prompt if say for example the user does not enter 1 or -1? Instead of using the else statement to output "This is not a valid input," I want it to prompt the user once again until they enter the desired input. I am not quite getting the desired out with the while loop.

var myShopping = ["Eggs", "Milk", "Potatoes", "Cereal", "Banana"];
var ord = prompt("Enter 1 for alphabetical order, " +
"and -1 for reverse order", 1);

if (ord == 1) {
    myShopping.sort();
    document.write(myShopping.join("<br />"));
} else if (ord == -1) {
    myShopping.sort();
    myShopping.reverse();
    document.write(myShopping.join("<br />"));
} else {
    document.write("That is not a valid input");
}

I am new here and currently learning JavaScript. In the code below, how can I get it to loop and still prompt if say for example the user does not enter 1 or -1? Instead of using the else statement to output "This is not a valid input," I want it to prompt the user once again until they enter the desired input. I am not quite getting the desired out with the while loop.

var myShopping = ["Eggs", "Milk", "Potatoes", "Cereal", "Banana"];
var ord = prompt("Enter 1 for alphabetical order, " +
"and -1 for reverse order", 1);

if (ord == 1) {
    myShopping.sort();
    document.write(myShopping.join("<br />"));
} else if (ord == -1) {
    myShopping.sort();
    myShopping.reverse();
    document.write(myShopping.join("<br />"));
} else {
    document.write("That is not a valid input");
}

• javascript

Share Improve this question Follow asked Jun 10, 2015 at 21:46 ChiefChief 96311 gold badge1515 silver badges3434 bronze badges 3

• 1 wrap it in a while loop? while(true){ your code here } – John Ruddell Commented Jun 10, 2015 at 21:49
• Just so you know, there's a special place in hell for people who use document.write. :P Also, prompt makes for a horrible UI, and is arguably entirely unnecessary in an HTML page. – cHao Commented Jun 10, 2015 at 21:56
• I'm currently following a book and those are the instrcutions given, but i do sometimes omit it and use console.log instead. @cHao – Chief Commented Jun 11, 2015 at 10:29

Add a ment  | 

3 Answers 3

Sorted by: Reset to default 1

var valid_ans = false;
while(!valid_ans) { // repeat this block until valid_ans is true
       // your code
       If (prompt===1 || prompt===-1) {
            valid_ans = true;
        }
  }

The above code should give you an idea. Keep in mind that your browser does not like multiple prompts. After two consecutive prompts the browser will ask the user if prompts should be suppressed.

this is basically pseudo code, but should get you on the right track.. dont want to give you everything! best way to learn is through trial and error :)

var myShopping = ["Eggs", "Milk", "Potatoes", "Cereal", "Banana"];
while(true){
   //prompt here
   if(ord == 1){
       //do stuff
       break;
   }
   else if(ord == -1){
       //do stuff
       break;
   }
   else {
       //bad input
   }
}

we dont want to create the myShopping variable every time you go through the loop, so we put that outside of the loop... the prompt has to be inside incase they put in a bad character so that it will prompt them again.

some notes: document.write is pretty old and looks really bad so you should probably try to e up with a better way to do that... you may also want to put the logic of your if statements in a function you call so your code is neat

if you want to put it in a function then I would probably do something like this.

var doStuff = function(userInput){
    if(userInput == 1){
       //do stuff
       return true;
   }
   else if(userInput == -1){
       //do stuff
       return true;
   }
   else {
       //bad input
       return false;
   }
};

var myShopping = ["Eggs", "Milk", "Potatoes", "Cereal", "Banana"];
while(true){
    //prompt here
    var ord = prompt(... etc.);
    var toEndLoop = doStuff(ord);
    if(toEndLoop){
        break;
    } else {
        // they dun goofed.. tell them it was bad input and the prompt will happen again
    } 
}

You could use a while loop like so:

...
var promptText = "Your text";
var input = prompt(promptText);
while(input !== "1" && input !== "-1"){
  input = prompt("Your answer was not correct\n"+promptText);
}

I am new here and currently learning JavaScript. In the code below, how can I get it to loop and still prompt if say for example the user does not enter 1 or -1? Instead of using the else statement to output "This is not a valid input," I want it to prompt the user once again until they enter the desired input. I am not quite getting the desired out with the while loop.

var myShopping = ["Eggs", "Milk", "Potatoes", "Cereal", "Banana"];
var ord = prompt("Enter 1 for alphabetical order, " +
"and -1 for reverse order", 1);

if (ord == 1) {
    myShopping.sort();
    document.write(myShopping.join("<br />"));
} else if (ord == -1) {
    myShopping.sort();
    myShopping.reverse();
    document.write(myShopping.join("<br />"));
} else {
    document.write("That is not a valid input");
}

I am new here and currently learning JavaScript. In the code below, how can I get it to loop and still prompt if say for example the user does not enter 1 or -1? Instead of using the else statement to output "This is not a valid input," I want it to prompt the user once again until they enter the desired input. I am not quite getting the desired out with the while loop.

var myShopping = ["Eggs", "Milk", "Potatoes", "Cereal", "Banana"];
var ord = prompt("Enter 1 for alphabetical order, " +
"and -1 for reverse order", 1);

if (ord == 1) {
    myShopping.sort();
    document.write(myShopping.join("<br />"));
} else if (ord == -1) {
    myShopping.sort();
    myShopping.reverse();
    document.write(myShopping.join("<br />"));
} else {
    document.write("That is not a valid input");
}

• javascript

Share Improve this question Follow asked Jun 10, 2015 at 21:46 ChiefChief 96311 gold badge1515 silver badges3434 bronze badges 3

• 1 wrap it in a while loop? while(true){ your code here } – John Ruddell Commented Jun 10, 2015 at 21:49
• Just so you know, there's a special place in hell for people who use document.write. :P Also, prompt makes for a horrible UI, and is arguably entirely unnecessary in an HTML page. – cHao Commented Jun 10, 2015 at 21:56
• I'm currently following a book and those are the instrcutions given, but i do sometimes omit it and use console.log instead. @cHao – Chief Commented Jun 11, 2015 at 10:29

Add a ment  | 

3 Answers 3

Sorted by: Reset to default 1

var valid_ans = false;
while(!valid_ans) { // repeat this block until valid_ans is true
       // your code
       If (prompt===1 || prompt===-1) {
            valid_ans = true;
        }
  }

The above code should give you an idea. Keep in mind that your browser does not like multiple prompts. After two consecutive prompts the browser will ask the user if prompts should be suppressed.

this is basically pseudo code, but should get you on the right track.. dont want to give you everything! best way to learn is through trial and error :)

var myShopping = ["Eggs", "Milk", "Potatoes", "Cereal", "Banana"];
while(true){
   //prompt here
   if(ord == 1){
       //do stuff
       break;
   }
   else if(ord == -1){
       //do stuff
       break;
   }
   else {
       //bad input
   }
}

we dont want to create the myShopping variable every time you go through the loop, so we put that outside of the loop... the prompt has to be inside incase they put in a bad character so that it will prompt them again.

some notes: document.write is pretty old and looks really bad so you should probably try to e up with a better way to do that... you may also want to put the logic of your if statements in a function you call so your code is neat

if you want to put it in a function then I would probably do something like this.

var doStuff = function(userInput){
    if(userInput == 1){
       //do stuff
       return true;
   }
   else if(userInput == -1){
       //do stuff
       return true;
   }
   else {
       //bad input
       return false;
   }
};

var myShopping = ["Eggs", "Milk", "Potatoes", "Cereal", "Banana"];
while(true){
    //prompt here
    var ord = prompt(... etc.);
    var toEndLoop = doStuff(ord);
    if(toEndLoop){
        break;
    } else {
        // they dun goofed.. tell them it was bad input and the prompt will happen again
    } 
}

You could use a while loop like so:

...
var promptText = "Your text";
var input = prompt(promptText);
while(input !== "1" && input !== "-1"){
  input = prompt("Your answer was not correct\n"+promptText);
}

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