Develop Reference

How do I get this script to multiply a number that was typed into the input field?

I'm trying to pull the number that a user types into a text field and multiply that by a number that is already established. (There are other buttons that add +1 or subtract -1 from the total that work just fine. The only problem I'm having is this right here, getting a user's input by them typing in a value to a field and pulling it)
Here's my code:
<!-- HTML Field that I am trying to pull a number out of -->
<input type="text" id="multNumInput">
--
// Creative my variables
var number = 0;
// Creative a variable that is equal to whatever is inputted into the text box
var multNum = $("#multNumInput").val();
// On Button Click, take the number variable and multiply it times whatever the value was inputted in the html
$('#multiply').click(function(){
number = number * multNum;
$('result1').text(number);
console.log(number);
})
Hopefully this is clear enough to understand. As of right now, whenever I click the button, it always changes the number back to 0. That's it. Just 0. No matter what I set the num var to, when clicking the mult button, it always reverts to 0.

You have to convert to number first.
multNum = parseInt(multNum);
number = number * multNum;
//...

First of all, the obvious: Multiplying any number with your number variable which has 0 value will lead to 0 at all times - I suppose you know this but was confused or missed that part, probably by confusing it to initialization of 0 before an addition process. Set it to 1 or another non-negative number and you will probably get better results on the way. :)
In addition, to make it multiply correctly in JS, you have to multiply between two numbers.
Your value is of type String as inserted in your input field.
As already suggested by #Si8, you need to parse it to Number by doing:
multNum = parseInt(multNum);
Also, you seem to be using a text type for your input.
I suggest you set it to a number type, so that you restrict input values:
<input type="number" id="multNumInput">
Check out the Mozilla MDN web docs for more on this.

The answer, as provided by #Robin Zigmond in a comment is this:
"You're failing to convert multNum from a string to a number."

Integer/decimal user input: how to serialize/store the value

Our stack is currently: React SPA/Apollo/GraphQL/Rails/PostgreSQL.
We have a web form with a number input that maybe (or not) be used to entry decimal values (dynamic/user-created form).
We want the form to be lenient (it has an autosave feature). If user types ,3 or 17,, that is considered a valid number value. But not too lenient, the number should by parseable as a float and be able to display in graphs...
Also, when the user visit the form again, we want to make sure to init the number input with the exact same value he typed initially (I mean, ,3 does not become magically 0,3)
I'd like to know, for our stack, how to serialize (sending as GraphQL payload) and store (in PostgreSQL) and manipulate (in JS/Ruby) such number without loosing the initial user input value.
I'm thinking it would be simpler to send/store a string, as long as it's validated that it can be parsed.
Just wondering if there is a "proper" solution, for example using number libs, custom GraphQL scalar type, decimal SQL type... that seems complicated to me, anyone did something similar before?

Create two fields. One for user input and other with parsed value. I do not think this will be different for any stack.
The challenge is how to show to a user how you understood entered value. This could be solved with a hint with a parsed value under the text field.

you should choose type of the input as "text" instead of number, so you can create a specific format for your input. first, add a property to your state
state={amount:""}
input section for amount in your form should be like this:
<input
type="text"
placeholder="Amount"
value={this.state.amount}
onChange={this.onAmountChange}
/>
onAmountChange = e => {
const amount = e.target.value;
if (!amount || amount.match(/^-?[0-9]\d*(\.\d{0,2})?$/)) {
this.setState(() => ({ amount }));
}
};
regexp in above function means start with any number with optional -, and optionally u can end with 2 decimal number. you can change it for your form.
if you want to add only positive numbers if your form is for price you can use this regexp:
amount.match(/^\d{1,}(\.\d{0,2})?$/)

AngularJS number input that ignores all keys but numbers

I've been trying to create an input in an AngularJS template and that will only accept whole numbers as input. That is, I don't want it to allow any keys other than 0-9, specifically, I can't stop . from being allowed in the input.
Alexander Puchkov created a directive that achieves this on inputs with type="text" however I want to be able to use type="number" so I can maintain all my other attributes on the field for validation such as min, max, step, etc.
I have an example of this directive not working on a number input here. For example, when type="text" an input of 123. yields a rendering of 123 however when type="number" an input of 123. yeilds 123. since the previous value of 123 is equal when compared numerically.

I'm afraid this simply isn't possible as the following condition is true:
0. == 0
If you perform the following:
setTimeout(() => console.log(element[0].value), 100))
It will always log 0. as 0. This is why ngModelCtrl isnt triggering the parser as no changes are detected.
I would suggest not directly modifying the value of ngModel (as this can also end up leading to users putting in invalid data. ie. pasting 12.00 will resolve to 1200 with your example)
I would add a directive that applies validity depending on if a decimal point is used (technically speaking, typing 0. isn't actually using it. 0.01 is). Set the validity to false if there is a decimal point in the number and display an error message accordingly (via ngMessages). This way the user can correct their own error and can learn from the mistake.

Obtain and check the value of an input text with javascript

I am fairly new with javascript and I need a script to obtain the value of an input text and check that value if it is equal to 0 (zero). If it does then I need an alert message notifying me that the text input is 0. Thanks.
<input id="txtVal" type="text" name="txtVal" value="0" maxlength="10">

The short answer:
if(txVal.value==0) alert('Please enter a number.');
Is not always the best answer:
var v=document.getElementById('txtVal');
v=parseInt(v,10);
if(v<=0) alert('Please enter a positive integer.');
Of course that probably not the best answer either but it does fix a couple of common mistakes.
Although you can refer to an element by using its id as a variable name its not recomended.
The value property of an input (ie txtVal.value) is a string (even if it contains only digits) so if you try to compare it to a number you may get unexpected results. In this case you are comparing it to 0 so problems are less likely but if you ever change your code to compare to another number you will probably run into problems, so its best to make it into an actual number before you do anything with it.
If you want to allow decimals use parseFloat instead.

Decimal Field Validation in Textbox with Jquery or Javascript

I searched on the forum but didn't find the correct answer.
What I am trying is
Textbox which accepts decimal numbers, so user should be able
to enter either 0 or 1 decimal point ie. dot(.)
at the max 5 digits before the dot and at the max 5 digits after the dot
no other character should be allowed, but arrow keys and other keys like f1 f2 should work
eg. it should be valid for following
12345
12345.1
12345.12345
1.12345
.12345
Need help in making this textbox.

Try this:
function isFloat(s) {
return s ? /\d{1,5}(?:\.\d{1,5})?/.test(s) : true;
}
$('input.float').on('change', function() {
if (!isFloat($(this).val())) {
alert('not a float');
}
});
And here's the fiddle: http://jsfiddle.net/foxbunny/Vabj4/
The code doesn't make the field required. If it's empty, it'll just pass. If you can change that by changing true in the ternary conditional to false (line 2).
EDIT:
Oh, and if you want to restrict input to certain keys, you should reconsider. It's not a very good user experience. People are used to typing just about anything. It's best to just warn them. It's cheaper to do and it's effective enough:
http://jsfiddle.net/foxbunny/Vabj4/1/