JavaScript string concatenation not working

Question

This javascript code to concatenate isn't working. I tried an alert before closure of script tag, it's displayed but the code below that I want to display the result in third or different text field.

HTML:

<input type="text" id="field"><br>
<input type="text" id="str2"><br>
<input type="text" id="str3"><br>
<button onclick="concate()">Concatenate</button>

JavaScript:

var s=document.getElementById("field").value;
var t=document.getElementById("str2").value;
var st=document.getElementById("str3").value;

function concate()
{
    st=s+t;
    document.getElementById("str3").value.innerHTML=st;
    console.log(st);
    document.write(st); 
}

For your information: w3schools.com/jsref/dom_obj_text.asp

Patrick Aleman
– Patrick Aleman

2016-02-18 10:03:26 +00:00
Commented Feb 18, 2016 at 10:03 — Patrick Aleman
– Patrick Aleman, Commented Feb 18, 2016 at 10:03

Zakaria Acharki · Accepted Answer · 2016-02-18 09:35:32Z

5

There's no function .value.innerHTML should be :

document.getElementById("str3").value = st;

Also you should get the fields value inside function and close your function definition using }, check example bellow.

Hope this helps.

function concate()
{
     var s=document.getElementById("field").value;
     var t=document.getElementById("str2").value;

     document.getElementById("str3").value=s+t;
}

<input type="text" id="field"><br>
<input type="text" id="str2"><br>
<input type="text" id="str3"><br>
<button onclick="concate()">Concatenate</button>

edited Feb 18, 2016 at 9:35

answered Feb 18, 2016 at 9:30

Zakaria Acharki

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2 Comments

fdomn-m Over a year ago

To confirm and clarify: when you get the values (in the question code), is when the script first runs (probably on load and most likely blank), not when you run concat. So any changes to the inputs occurs after you have already populated s and t. By putting them inside the function, you read the current values when the function is called.

Zakaria Acharki Over a year ago

Thenks @freedomn-m for your intervention don't hesitate to edit the post directely by adding your explication.

Transformer · Accepted Answer · 2016-02-18 10:04:41Z

0

function concate() {
    var s=document.getElementById("field").value;

    var t=document.getElementById("str2").value;

    var st=document.getElementById("str3").value;
    // this is a standard way to concatenate string in javascript
    var result = s+t;
    document.getElementById("str3").value=result;

}

<input type="text" id="field"><br>
<input type="text" id="str2"><br>
<input type="text" id="str3" readonly><br>
<button onclick="concate()">Concatenate</button>

edited Feb 18, 2016 at 10:04

answered Feb 18, 2016 at 9:39

Transformer

3,7701 gold badge25 silver badges33 bronze badges

6 Comments

Qwertiy Over a year ago

Why do you use concat instead of +?

fdomn-m Over a year ago

"This is a standard way to concatenate string in javascript" - no, it's not.

Patrick Aleman Over a year ago

.concat() is used for Arrays, for strings you use the +

Transformer Over a year ago

maybe i should delete the answer then??

Vincent1989 Over a year ago

@Transformer you can read refer to this stackoverflow.com/questions/16124032/…

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