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How to validate the select method with submit type?

I want to validate the select method with submit type button. I have created a form and under that, I have created the select method and given some options. By submit type, the onClick should validate my submit type with the options in the select method. How can I assign the value of option
to var t based on select?
According to the select option my var t should be changed.
If the value is volvo then it should print val11, similarly Saab= val14, opel= val82, Audi= val34
<select name="carlist" class="temp>
<option value="10">Volvo</option>
<option value="20">Saab</option>
<option value="30">Opel</option>
<option value="45">Audi</option>
</select>
<input type="submit" class="temp" value="submit the answer">
<script>
var t;
if () {
t=value;
} else if () {
t=value;
} else if () {
t=value;
}else {
t=value;
}
</script>

You can call a function on clicking the button. Inside the function get the text of the selected option:
function getValue(){
var el = document.querySelector('.temp');
var val = el.options[el.selectedIndex].text;
var t;
if(val == "Volvo")
t = 'val11';
else if(val == "Saab")
t = 'val14';
if(val == "Opel")
t = 'val82';
else if(val == "Audi")
t = 'val34';
alert(t);
}
<form>
<select name="carlist" class="temp">
<option value="10">Volvo</option>
<option value="20">Saab</option>
<option value="30">Opel</option>
<option value="45">Audi</option>
</select>
<input onclick="getValue()" type="submit" class="temp" value="submit the answer">
</form>
You can also think of using data attribute which is more cleaner and simpler:
function getValue(){
var el = document.querySelector('.temp');
var t = el.options[el.selectedIndex].getAttribute('data-val');
alert(t);
}
<form>
<select name="carlist" class="temp">
<option value="10" data-val="val11">Volvo</option>
<option value="20" data-val="val14">Saab</option>
<option value="30" data-val="val82">Opel</option>
<option value="45" data-val="val34">Audi</option>
</select>
<input onclick="getValue()" type="submit" class="temp" value="submit the answer">
</form>

You can do a few things, here's the simplest I could get away with.
function submitForm() {
const value = document.querySelector('[name="carlist"').value;
console.log(value);
return false; // to prevent it navigating away.
}
<form onsubmit="submitForm()">
<select name="carlist" class="temp">
<option value="1">Volvo</option>
<option value="2">Saab</option>
<option value="3">Opel</option>
<option value="4">Audi</option>
</select>
<input type="submit" class="temp" value="submit the answer">
You can also have some validation running earlier, e.g. on change:
/**
* This function runs on form submit.
*/
function submitForm(event) {
const value = document.querySelector('[name="carlist"').value;
console.log(value);
// to prevent it navigating away.
event.preventDefault();
return false;
}
/**
* This function runs on selection change
*/
function validateCar(changeEvent) {
console.log('Change');
// do something with changeEvent
}
<form onsubmit="submitForm(event)">
<select name="carlist" class="temp" onchange="validateCar(event)">
<option value="1">Volvo</option>
<option value="2">Saab</option>
<option value="3">Opel</option>
<option value="4">Audi</option>
</select>
<input type="submit" class="temp" value="submit the answer">

You can set an id attribute on the select element and then access it through a querySelector or getElementById.
<form id="carForm">
<select name="carlist" class="temp" id="car">
<option value="val11">Volvo</option>
<option value="val14">Saab</option>
<option value="val82">Opel</option>
<option value="val34">Audi</option>
</select>
</form>
let carForm = document.getElementById('carForm');
carForm.onsubmit = function(event) {
var t = document.getElementById('car');
...
}
See codepen example

Second dropdown value is not changing if I doesn't change my first dropdown

I am trying to show a table of reviews by taking the value of two dropdowns. When I was having one dropdown(positive, negative etc) that works fine but when I introduce another dropdown(food, drinks etc) it is not working.
It only works when I change the first dropdown and second dropdown but if I kept the first dropdown unchanged then it's not working
I tried by adding onchange method to the second dropdown. I just started with Javascript so not much idea about what to try.
function printResult(form) {
var output = {
{
output | safe
}
};
var sel = form.list;
var sel2 = form.list2;
var selectedVal = sel.options[sel.selectedIndex].value;
var selectedVal2 = sel2.options[sel.selectedIndex].value;
//document.getElementById("showResult").innerText = "Your number is: " + selectedVal;
//console.log(output);
document.getElementById("showResult").innerText = "Your number is: " + selectedVal2;
}
<form action="dropdown" onSubmit="return printResult(this);">
<label for="sentiment">Sentiment</label>
<div class="styled-select blue semi-square">
<select name="list">
<option value="all">All</option>
<option value="positive">Positive</option>
<option value="negative">Negative</option>
<option value="neutral">Neutral</option>
</select>
</div>
<div>
<select name="list2" onChange="printResult()">
<option value="menu">Menu Range</option>
<option value="food">Food</option>
<option value="drinks">Drinks</option>
<option value="desserts">Desserts</option>
</select>
</div>
<input type="submit" value="Filter">
<span id="showResult"></span>
</form>

You need to pass the form on the change too and return false to not submit the form:
function printResult(form) {
var sel = form.list;
var sel2 = form.list2;
var selectedVal = sel.value;
var selectedVal2 = sel2.value;
document.getElementById("showResult").innerText = "Your number is: " + selectedVal2;
return false;
}
<form action="dropdown" onSubmit="return printResult(this);">
<label for="sentiment">Sentiment</label>
<div class="styled-select blue semi-square">
<select name="list">
<option value="all">All</option>
<option value="positive">Positive</option>
<option value="negative">Negative</option>
<option value="neutral">Neutral</option>
</select>
</div>
<div>
<select name="list2" onChange="printResult(this.form)">
<option value="menu">Menu Range</option>
<option value="food">Food</option>
<option value="drinks">Drinks</option>
<option value="desserts">Desserts</option>
</select>
</div>
<input type="submit" value="Filter">
<span id="showResult"></span>
</form>
Perhaps you wanted this instead
window.addEventListener("load", function() {
document.getElementById("form1").addEventListener("submit", function(e) {
e.preventDefault(); // stop submission
var sel = this.list;
var sel2 = this.list2;
var selectedVal = sel.value;
var selectedVal2 = sel2.value;
document.getElementById("showResult").innerText = (selectedVal && selectedVal2) ? selectedVal + ":" + selectedVal2 : "Please select both";
});
});
<form action="dropdown" id="form1">
<label for="sentiment">Sentiment</label>
<div class="styled-select blue semi-square">
<select name="list">
<option value="">All</option>
<option value="positive">Positive</option>
<option value="negative">Negative</option>
<option value="neutral">Neutral</option>
</select>
</div>
<div>
<select name="list2">
<option value="">Menu Range</option>
<option value="food">Food</option>
<option value="drinks">Drinks</option>
<option value="desserts">Desserts</option>
</select>
</div>
<input type="submit" value="Filter">
<span id="showResult"></span>
</form>

Pass dropdown values to text box with javascript

I don't know much about javascript and unfortunately don't have time to learn before this project is due (wish I did!). I assume it is possible to pass the value of a drop-down selection into a hidden text input field on a form before the form is submitted. Could anyone help me figure out how to do that with javascript? Thank you! Here are my drop-down and text box details:
<div class="formEntryArea">
<div class="formEntryLabel">
<span class="formLabel"><label for=" langdropdown">Would you like to receive library notices in English or Spanish? ><span class="formRequired">*</span></label></span>
</div>
<div class="formMultiSelect" id=”langdropdown”>
<select name=" langdropdown ">
<option value="0" selected="selected">Choose language</option>
<option value="eng">English</option>
<option value="spa">Spanish</option>
<input type="text" id="ddepartment" name="ddepartment" value=””>
</select>
</div>

This is simply. First of all, you have to bind a change event handler for your select. Then, you have to set input text with value selected from dropdown.
var select=document.getElementsByTagName('select')[0];
var input=document.getElementById('ddepartment');
select.onchange=function(){
input.value=select.options[select.selectedIndex].text;
}
<div class="formEntryArea">
<div class="formEntryLabel">
<span class="formLabel"><label for=" langdropdown">Would you like to receive library notices in English or Spanish? ><span class="formRequired">*</span></label></span>
</div>
<div class="formMultiSelect" id=”langdropdown”>
<select name=" langdropdown ">
<option value="0" selected="selected">Choose language</option>
<option value="eng">English</option>
<option value="spa">Spanish</option>
</select>
<input type="text" id="ddepartment" name="ddepartment">
</div>

You can use this code:
var myselect = document.getElementById("MySelect");
myselect.onchange = function(){
alert(myselect.options[myselect.selectedIndex].value);
document.getElementById("ddepartment").value = myselect.options[myselect.selectedIndex].value;
};
Result: https://jsfiddle.net/fh5myefw/

Mind to close the tags, it's better practice.
var select = document.getElementById('selectElem');
var outputElem = document.getElementById('ddepartment');
select.addEventListener('change',function(){
var newValue = !this.selectedIndex ? "":this.options[this.selectedIndex].text;
outputElem.value = newValue;
});
<select name="langdropdown" id="selectElem" required>
<option value="" selected="selected">Choose language</option>
<option value="eng">English</option>
<option value="spa">Spanish</option>
</select>
<input type="text" id="ddepartment" name="ddepartment" value="">

this is javascript function
function func(selectObject)
{
document.getElementById('ddepartment').value = selectObject.value;
}
add onchange event to select element like this
<select name="langdropdown" onchange="func(this)">

Here use this:
var sel = document.getElementById('lang');
sel.onchange = function() {
var val = this.options[this.selectedIndex].value;
var che = document.getElementById('cache').value;
che = val;
console.log(che);
}
SNIPPET
var sel = document.getElementById('lang');
sel.onchange = function() {
var val = this.options[this.selectedIndex].value;
var che = document.getElementById('cache').value;
che = val;
console.log(che);
}
<select id='lang' name="lang">
<option value="" selected>Choose language</option>
<option value="eng">English</option>
<option value="spa">Spanish</option>
<option value="jpn">Japanese</option>
<option value="zho">Chinese</option>
<option value="fin">Finnish</option>
<option value="nav">Navajo</option>
</select>
<input type="hidden" id="cache" name="cache" value=””>

Need to show two separate info on one select HTML/JS

I need to show these two array in two text field when selecting one option.
What is happening now is its just showing the first array, it needs to show two array on the input tags when creating country is selected.
var host_country_start = {
"Afghanistan":"21-Dec_start",
"Albania":"01-Jan_start",
"Algeria":"01-Jan_startz",
};
var host_country_end = {
"Afghanistan":"21-Dec_end",
"Albania":"test_end",
"Algeria":"test2_end",
};
var selectbox = document.getElementById('host_country');
var textbox = document.getElementById('host_country_date');
selectbox.addEventListener('change', function(e){
textbox.value = host_country_start[this.value]
})
<span id="s_home_country">
<select name="Host Country" id="host_country">
<option value="Select one" selected="selected">Select one</option>
<option value="Afghanistan">Afghanistan</option>
<option value="Albania">Albania</option>
<option value="Algeria">Algeria</option>
</select>
</span>
<label>Start Date:</label><input id="host_country_date" type="text" />
<label>End Date:</label><input id="host_country_end_date" type="text" />

You have to add the reference to the another array and include it in your code.
var host_country_start = {
"Afghanistan":"21-Dec_start",
"Albania":"01-Jan_start",
"Algeria":"01-Jan_startz",
};
var host_country_end = {
"Afghanistan":"21-Dec_end",
"Albania":"test_end",
"Algeria":"test2_end",
};
var selectbox = document.getElementById('host_country');
var textbox = document.getElementById('host_country_date');
var textbox2 = document.getElementById('host_country_end_date');
selectbox.addEventListener('change', function(e){
textbox.value = host_country_start[this.value];
textbox2.value = host_country_end[this.value];
})
<span id="s_home_country">
<select name="Host Country" id="host_country">
<option disabled value="Select one" selected="selected">Select one</option>
<option value="Afghanistan">Afghanistan</option>
<option value="Albania">Albania</option>
<option value="Algeria">Algeria</option>
</select>
</span>
<label>Start Date:</label><input id="host_country_date" type="text" />
<label>End Date:</label><input id="host_country_end_date" type="text" />

You just need to get a reference to the second text field and add an additional line of code in your event handler that sets its value using the same technique as you did with the first textbox, but accessing the second array instead of the first.
var host_country_start = {
"Afghanistan":"21-Dec_start",
"Albania":"01-Jan_start",
"Algeria":"01-Jan_startz",
};
var host_country_end = {
"Afghanistan":"21-Dec_end",
"Albania":"test_end",
"Algeria":"test2_end",
};
var selectbox = document.getElementById('host_country');
var start = document.getElementById('host_country_date');
var end = document.getElementById('host_country_end_date');
selectbox.addEventListener('change', function(e){
start.value = host_country_start[this.value];
end.value = host_country_end[this.value];
})
<span id="s_home_country">
<select name="Host Country" id="host_country">
<option value="Select one" selected="selected">Select one</option>
<option value="Afghanistan">Afghanistan</option>
<option value="Albania">Albania</option>
<option value="Algeria">Algeria</option>
</select>
</span>
<label>Start Date:</label><input id="host_country_date" type="text" />
<label>End Date:</label><input id="host_country_end_date" type="text" />

Onclick Navigation

<select id="drp" value="maindrp" name="maindrp">
<option>Select Categories</option>
<option id="vhc" value="mainvhc">Vehicles</option>
<option id="re" value="mainre">Real Estate</option>
<option id="pt" value="mainpt">Pets</option>
<option id="el" value="mainel">Electronics</option>
<option id="cl" value="maincl">Clothing&Jewerly</option>
<option id="co" value="mainco">Computers&Network</option>
</select>
<input type="text" placeholder="Search" id="msc">
<input type="submit" value="Go" id="go" onclick= "go();">
function go() {
if (document.getElementById("vhc")) {
window.location="vehicles.php";
}else if (document.getElementById("re")) {
window.location="realestate.php"; } }
I want to navigate from selected item from drop down via button on click function.
Can anyone help me please?

Try this, you need the value of <select> tag
function go(){
var sel = document.getElementById('drp').value; // get value of <select>
if(sel=='mainvhc')
window.location.href='vehicles.php';
...
}