How to enter value in text box using Jmeter without post request

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How to enter value in text box using Jmeter without post request
I am building Jmeter test plan, in website I have one text both and as soon as I enter any value in textbox, it calculates something and populate one value. Here there is no post/get request. So how can I input some value in such case?
I even recorded everything but did not see that value is posting so somehow I will have to enter value into textbox via jmeter without get/post.
In below screenshot 880 is value which I want to insert via Jmeter.

Html code of text box is :
<input type="number" class="form-control amount_value" id="x_amount" name="amount" placeholder="Number of values" required="required" onkeyup="getprice('SIP','sip-amount',this.value,'4.5556665565')">
@KirilS. - You are correct but here I have to post populated value via API post request and to populate some value it is mandatory to insert some value in text box.
– Helping Hands
Aug 10 at 19:15
on UI - yes, but JMeter works below UI on HTTP level. So just populate value directly into post request, forget about input boxes, they don't exist for JMeter.
– Kiril S.
Aug 10 at 20:45
1 Answer
1
As per JMeter project main page:
JMeter is not a browser, it works at protocol level. As far as web-services and remote services are concerned, JMeter looks like a browser (or rather, multiple browsers); however JMeter does not perform all the actions supported by browsers. In particular, JMeter does not execute the Javascript found in HTML pages. Nor does it render the HTML pages as a browser does (it's possible to view the response as HTML etc., but the timings are not included in any samples, and only one sample in one thread is ever displayed at a time).
So you have 2 options:
getprice()
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The goal of JMeter test is to create load on server side. In this case it seems operation is client-side only, there's no traffic to the server, hence this operation does not add any load on the server side and does not need to be tested during load test. SO what is the goal here then?
– Kiril S.
Aug 10 at 18:51