Set value of element using an input variable

Question

I have a js function that sets the value of id_2 based on the value of id_1. It looks like this below:

function set_value(id_1, id_2, url){
    var id_1_value;
    id_1_value = $(id_1).val();
    var value;
    ...
    /* calculation etc. */
    document.getElementById(id_2).value = value;
};

The function is linked to the id_1 html element by an onchange method like this onchange='set_value(this, id_2)'.

If I change the value in id_1 the function doesn't work and I get the following error in the console:

Unable to set property 'value' of undefined or null reference

but if I hardcode document.getElementById('id_2') in the function it works fine. How do I write this function so I can pass an element id variable to it successfully? I want to reuse this function for different elements you see...

Sorry that was an error, just changed it

DrBuck
– DrBuck

2016-05-04 10:00:23 +00:00
Commented May 4, 2016 at 10:00 — DrBuck
– DrBuck, Commented May 4, 2016 at 10:00

AsgarAli · Accepted Answer · 2016-05-04 10:01:13Z

1

Your set_value function should be as below.

function set_value(id_1, id_2, url) {
    var id_1_value = $(id_1).val();
    /* calculation etc. */
    if ($(id_2).length !== 0)
    {
        $(id_2).val(id_1_value);
    }
}

answered May 4, 2016 at 10:01

AsgarAli

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1 Comment

DrBuck Over a year ago

Thanks I'm going for this one because I want to avoid having to add quotes to my input variable. The onchange=set_value(this, id_2) part is autogenerated using my django code

Riddell · Accepted Answer · 2016-05-04 09:58:32Z

0

Are you passing "#id_2" to the set_value parameter?

if so that means it would return null.

// The function should be called like this 
 var id_2 =  "id_2";
 set_value(this, id_2, blah...)

answered May 4, 2016 at 9:58

Riddell

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Comments

Pawan Nogariya · Accepted Answer · 2016-05-04 10:01:26Z

0

Change the call like this

onchange='set_value(this, "id_2")'

Second parameter should be passed as string.

answered May 4, 2016 at 10:01

Pawan Nogariya

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Tuan-IT · Accepted Answer · 2016-05-04 10:04:15Z

0

try this following code:

function set_value(id_1, id_2, url){
    var id_1_value = $(id_1).val();
    var value;
    ...
    /* calculation etc. */
    document.getElementById(id_2).value = value;
};

and onchange function

onchange="set_value(this, 'id_2')"

answered May 4, 2016 at 10:04

Tuan-IT

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