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Question

I have made a function and captured the value of a textbox. On a button click, it should alert the value. The code is:

function substitute (argument) {
    var myVal=document.getElementById('myTextBox').value();
    alert(myVal);
    if (myVal.length==0) {
        alert('Empty Textbox');
    };
}

It is then executed using this:

<input type="button" name="Button" value="Click Me" onclick="substitute();">

But nothing happens. Please tell me where am I doing it wrong.

Answer 1

You have a few errors:

1. .value() is not a function: use .value
2. You don't need that semicolon at the end of the if statement
3. Your text box might not have the id that you're referring to: make sure that you have id="myTextBox" in the opening tag
4. While it won't cause any errors, your function definition lists a parameter, but you do not pass one when you call it.

Always check your browser console for errors if nothing is happening. Always.

function substitute () { // Parameter "argument" is not necessary
    var myVal=document.getElementById('myTextBox').value; //.value, not .value()
    alert(myVal);
    if (myVal.length==0) {
        alert('Empty Textbox');
    }; // You don't need this semicolon
} // You were missing this curly brace

Demo

Answer 2

value is not a function, it's a property, therefore:

var myVal=document.getElementById('myTextBox').value;

As you're brand new to JS, I'll give you a piece of advice: If you want to manipulate the DOM, use jQuery .

Answer 3

In Your code, you are not passing any parameter to function subsititute(), But @ function definition you wrote substitute(argument). Thats a big issue, and also you put there is a semi-column after if condition inside the function. No need of it

Try This..

<input type="text" id="myText" value="Hello" />
<input type="button" name="Button" value="Click Me" onclick="substitute();" />

In script part,

function subsitute()
{
  var myVal=$('#myText').val();
  alert(myVal);
  if (myVal=='')
  {
    alert('Empty Textbox');
  }
}

Answer 4

http://jsbin.com/tewudopi/1/edit

Add an ID to the button. When referencing the button, it is not ".value()", it is simply ".value".

As a side note, you should use === instead of == to compare.

function substitute() {
  var myVal=document.getElementById('myTextBox');
  alert(myVal.value);
  if (myVal.value.length===0) {
    alert('Empty Textbox');
  }
}

Answer 5

Maybe something like the following.

<script type="text/javascript">
function substitute() {

var myVal=document.getElementById('myTextBox').value;
if (myVal.length>0) {
alert(myVal);
}
if (myVal.length==0) {
    alert('Empty Textbox');
}
}
</script>
<input type="button" name="Button" value="Click Me" onclick="substitute();">
<textarea name="myTextBox" id="myTextBox"></textarea>

Fiddle demo