Javascript Input Checker

Question

I have a name input checker using Javascript and I'm struggling to see the issue. When the input has been entered and matches the array, the site should return ("Welcome" . inputValue) as an alert. However, I am getting an alert but it only says "undefined". If the person types in the incorrect name (doesn't match the array) it does feedback "User not know" As it is meant to. So the only issue is when the input value matches the array it gives the result "undefined".

var x = ["Bob", "James", "Alan", "Emilie", "Donna", "Ashleigh", "Arthur", "John"];


function checkInput() {

  var inputValue = document.getElementById("inputString").value;

  var test = x.indexOf(inputValue);

  if (test >= 0)
    alert("Welcome ".inputValue);

  else
    alert("User not known");

}

<form>
  <input type="text" id="inputString">

  <button onclick="checkInput()">Evaluate input</button>
</form>

JavaScript is not PHP; the string-concatenation is the + operator, not the period (.). — David Thomas
– David Thomas, Commented Oct 13, 2020 at 16:04

Derek Wang · Accepted Answer · 2020-10-13 16:06:46Z

1

The message format on alert function when matched is invalid.

It is needed to "Welcome " + inputValue instead of "Welcome ".inputValue. On javascript, to join string, + operator is used.

var x = ["Bob", "James", "Alan", "Emilie", "Donna", "Ashleigh", "Arthur", "John"];

function checkInput(event) {
  var inputValue = document.getElementById("inputString").value;
  var test = x.indexOf(inputValue);
  if (test >= 0)
    alert("Welcome " + inputValue);
  else
    alert("User not known");
}

<form>
  <input type="text" id="inputString">

  <button onclick="checkInput(event)">Evaluate input</button>
</form>

answered Oct 13, 2020 at 16:06

Derek Wang

10.2k4 gold badges20 silver badges40 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

sp00m Over a year ago

Just for the record, "Welcome ".inputValue is syntactically valid: it's reading the property inputValue on the string object "Welcome ", which is undefined (hence no error is being thrown, but undefined is alerted).

Collectives™ on Stack Overflow

Javascript Input Checker

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related