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How do you pass a value to a hidden form field when a certain option is selected?

I am new to javascript and cannot find an easy-to-understand answer.
I would like a certain value to get passed to a hidden field when a user selects a certain option from the select dropdown.
I know that there are if/else statements but I'm not sure if that would be used in this situation.
For example: I have a select dropdown of a list of states.
<select name="HomeState" required>
<option value="1">Alabama</option>
<option value="1">Alaska</option>
<option value="1">Arizona</option>
<option value="1">Arkansas</option>
<option value="5">California</option>
<option value="1">Colorado</option>
<option value="1">Connecticut</option>
<option value="1">Delaware</option>
</select>
As you can see, any option other than California will be rated at a value of 1.
I would like it to where if the user selects the option of California, then the value of $300 will get passed to a hidden form field.
<input name="AmountNeeded" type="hidden" value="300" />
If they select anything other than California, the hidden field would get passed $100
<input name="AmountNeeded" type="hidden" value="100" />
How would I implement this logic? Would it be using if/else statement? I am new and don't exactly know how to set that up.

To keep this simple you could assign ids to the <select> and hidden <input> and listen to the change event via onchange() on the <select> with a function call.
And based on the selected item, change the value of hidden input.
NOTE: To test the snippet out I have removed the type="hidden". Do place it back.
function homeSelected(){
const home = document.getElementById("homeSelector").value;
if(home == 5){
document.getElementById("amountNeeded").value = 300;
}else{
document.getElementById("amountNeeded").value = 100;
}
}
<select id="homeSelector" name="HomeState" onchange="homeSelected()" required>
<option value="1">Alabama</option>
<option value="1">Alaska</option>
<option value="1">Arizona</option>
<option value="1">Arkansas</option>
<option value="5">California</option>
<option value="1">Colorado</option>
<option value="1">Connecticut</option>
<option value="1">Delaware</option>
</select>
<input id="amountNeeded" name="AmountNeeded" value="100" />

You can do this as follows:
<select name="HomeState" required onChange=myFunction(this)>
<option value="1">Alabama</option>
<option value="1">Alaska</option>
<option value="1">Arizona</option>
<option value="1">Arkansas</option>
<option value="5">California</option>
<option value="1">Colorado</option>
<option value="1">Connecticut</option>
<option value="1">Delaware</option>
</select>
Javascript code is:
<script>
function myFunction(x) {
val = x.options[x.selectedIndex].text;
if(val == 'California')
document.getElementsByName("AmountNeeded")[0].value = 300
else
document.getElementsByName("AmountNeeded")[0].value = 100
}
</script>
If else statement is good for you if you are sure that All other states have value 1 except California. If all states may have different values like some states may have 1 or some may have 2 or some may have 3, then there may be other alternatives to solve this like you can pass give one more attribute data-src-amount to options and give amount to data-src-amount. You can create options like <option value="1" data-src-amount="100">Alabama</option> and in script, you can fetch data-src-amount on select change event instead of if-else statement.

Validation for select field angular 2

I am using angular2#2.4.1 release. How would i do a validation on select field?
<div class="form-group" [class.has-error] = "schoolError">
<label class="control-label" for="lang">Select School</label>
<select class="form-control" name="school"
required #school
[(ngModel)] = "model.school">
<option value="default">Select a school</option>
<option *ngFor= "let sch of school">{{sch}}</option>
</select>
</div>
<button class="btn btn-primary"
[disabled] = "form.invalid" type="submit">Submit</button>
Basically i want to disable the button when the select field is invalid? How do i make the select field invalid when no value is selected?

You can make a boolean variable and assign to it false as default value. When user chooses any option, it will turn true.
https://plnkr.co/edit/yR5xz4h3llkxHsUQxFJB?p=preview
<div>
<select [(ngModel)]='selected'>
<option value='one'>Three</option>
<option value='two'>Two</option>
</select>
<button [disabled]='!selected && form.status == 'VALID'>click</button>
</div>
selected:boolean = false;

Try changing the value in your default option to an empty string:
<option [value]="">Select a school</option>

I run into the same kind of situation and the below snippet seems to work pretty good.
<option [ngValue]="undefined">Select a school</option>

When adding ngForm to your name for your form your validation should work. I assume that is missing, because otherwise your form validation would work as is. So the only thing you would need is to add to your formtag is the aforementioned ngForm, like so:
<form #form="ngForm">
Here's a plunker

I believe you should be able to implement a [disabled]="checkSelectFunction()" on your button and then create a function to check if no value is chosen in the select field.

I am a little late here but the one thing that worked for me was setting the properties to null in the component.
For example,
HTML:
<div class="form-group">
<label for="type">Type</label>
<select
class="form-control"
id="type"
name="type"
[(ngModel)]="appointment.typeId"
required>
<option *ngFor="let aType of types"
[value]="aType.appointmentTypeId">
{{aType.type}}
</select>
Component:
appointment : Appointment = new Appointment(null);
Where model is:
export class Appointment {
constructor(
public typeId: number
) {}
}
I hope this helps someone like me who is new to Angular

I tried to give a value to option of the select like
<select id="something" formControlName="something">
<option value="something">Something</option>
</select>
The value of the option should not be an empty - if it's empty this required field counts as invalid.

Print only selected item from drop down

I have a select input on my page. When I print the page all the options of select get printed instead of the one that is selected. How do I make it so that only the option selected is printed?
<select class="form-control" id=myID onchange="update_status(this)">
<option value="1" selected>Pending</option>
<option value="2">Under-Preparation</option>
<option value="3">Delivered</option>
</select>

Print the selected choice's value like following snippet. Run code snippet for demonstration.
function update_status(selected_option){
console.log(selected_option.value);
}
<select class="form-control" id=myID onchange="update_status(this)">
<option value="s1" selected>Pending</option>
<option value="s2">Under-Preparation</option>
<option value="s3">Delivered</option>
</select>

It works fine...
javascript print() funtion just shows the rendered[visible] items in pdf preview.
Here is example you can visualize.
This might helps. Have fun.

This can be done as below-
function update_status(currentObj){
console.log(currentObj.options[currentObj.selectedIndex].value);
}
JS Fiddle
Thanks !!

Add a this.value instead this, checkout the snippet.
function update_status(vm) {
console.log(vm);
}
<select class="form-control" id=myID onchange="update_status(this.value)">
<option value="1" selected>Pending</option>
<option value="2">Under-Preparation</option>
<option value="3">Delivered</option>
</select>

Add value to a drop down menu with a form

Is there a way to insert values in a drop down menu with a simple form? I have this drop down menu
<form>
<select name="users" onchange="showUser(this.value)">
<option value="">Select a category:</option>
<option value="movie">Movie</option>
<option value="musik">Musik</option>
<option value="books">Books</option>
<option value="images">Images</option>
</select>
</form>
Should I use an array? I been searching the net but couldn't find anything that would help.

Here is a JavaScript solution to add items to a drop down.
The HTML to use..
<form>
<select id="categories" name="users" onchange="showUser(this.value)">
<option value="">Select a category:</option>
<option value="movie">Movie</option>
<option value="musik">Musik</option>
<option value="books">Books</option>
<option value="images">Images</option>
</select>
</form>​​
JavaScript code...
var categories = document.getElementById("categories");
var newOption = document.createElement('option');
newOption.innerText = "New value";
newOption.setAttribute('value', 'newvalue');
categories.appendChild(newOption);
​
jQuery code... (a lot shorter)
$("#categories").append("<option value='newvalue'>New Value</option>");
Here is the JavaScript JSFiddle and the jQuery JSFiddle to play with!

You could look into jQuery append() and option() with click event...
I've just created a working solution for you.
Don't know if this is what you was looking for, but this is how it works:
You simply just write the value and visual option name into a form text field: value, text which gives you this:
<option value="value">text</option>
<select id="mySelect"></select>
<p> </p>
<input type="text" id="string"><br>
<button id="append">Append</button>
$('#append').click(function(){
var str = $('#string').val();
var substr = str.split(', ');
$('#mySelect').append( new Option(substr[0],substr[1]));
});
Here is a working version: http://jsfiddle.net/SCf8m/1/

dropdown menu to create text field

I have spent about an hour or two trying to find out how to use JavaScript to create a text field when a certain value is selected from a drop down list.
Here is the code for the drop down menu if that's of any help. I'd have attempted to write the code to do this myself, but I am still very unfamiliar with how to write JavaScript code
<select name="claim">
<option value="">Select a Claim</option>
<option value="Insurance">Insurance</option> // this option I want when selected to create a text field
<option value="Warranty">Warranty</option>
</select>

try this hope it helps
<div id="area">
<select id="claim" name="claim">
<option value="">Select a Claim</option>
<option value="Insurance">Insurance</option>
<option value="Warranty">Warranty</option>
</select>
</div>
and script
$(document).ready(function(){
$("#claim").change(function(){
$("#area").find(".field").remove();
//or
$('#area').remove('.field');
if( $(this).val()=="Insurance")
{
$("#area").append("<input class='field' type='text' />");
}
});
});
example http://jsfiddle.net/cqjJy/