how to get the value of a function from a button click in javascript?

Question

i am new to javascript and am trying to go through tutorials to understand the concepts.

this is my function

function toCelsius(fahrenheit){

    (5/9) * (fahrenheit-32);    
    document.getElementById("demoTemp").onclick.toString();

}

and i am trying to invoke it here:

<form>
<br>
Enter number: <input type="text" name="firstname">

<!-- <input type="text" name="lastname"> -->
<button type="button" onclick="toCelsius()"> new temp in Celsius </button>
</form>

<p id="demoTemp"></p>

i want the user to be able to enter a value and then hit the button that will tell them their new temperature from fahrenheit to celsius

Elegant way is first attach a 'click' event listener to required button. [developer.mozilla.org/en-US/docs/Web/API/… Then perform your logic as per one of the following answers. It is important to understand event binding first. Also explore that event object. — Pranav
– Pranav, Commented Nov 27, 2014 at 10:56

Amit Joki · Accepted Answer · 2014-11-27 10:51:58Z

4

Just put the result in the inner html.

function toCelsius(){
    var fahrenheit = document.getElementsByName("firstname")[0].value;
    var cel = (5 / 9) * (fahrenheit - 32);    
    document.getElementById("demoTemp").innerHTML = cel;
}

edited Nov 27, 2014 at 10:51

answered Nov 27, 2014 at 10:45

Amit Joki

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1 Comment

Benjamin Poignant Over a year ago

He dont want pass fahrenheit, but get input value, use document.getElementById("id").val and add id id at your input

Prakhar Asthana · Accepted Answer · 2014-11-27 10:50:52Z

0

You should make your function in this way :

  function toCelsius(){    var fahrenheit = document.getElementById('firstname').value; var cel=     (5/9) * (fahrenheit -32);        document.getElementById("demoTemp").innerHTML = cel;}

answered Nov 27, 2014 at 10:50

Prakhar Asthana

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Comments

Pankaj Goyal · Accepted Answer · 2014-11-27 10:54:43Z

0

You do not need to pass anything in the function. Try this JS :-

function toCelsius(){
    var fahrenheit = document.getElementsByName("firstname")[0].value;
    var cel = (5 / 9) * (fahrenheit - 32);    
    document.getElementById("demoTemp").innerHTML = cel;
}

answered Nov 27, 2014 at 10:54

Pankaj Goyal

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