Develop Reference

Finding variable types from a string

Pardon if this question has already been answered however I'm struggling to find the any answers to it.
I'm looking to see if I can convert variable types to a string in the code below.
input = prompt('Type something please', 'your input here')
alert(input + ' is a ' + typeof input)
i.e. if the user were to type 1 typeof would return number, or if the user were to enter true it would return a boolean

You can run the input through a series of parseInt, parseFloat and
parseBool
functions.
Whenever you get a valid result, return it.
Something similar to:
if (parseInt(input) != NaN) {
return "int"
}
if (parseFloat(input) != NaN) {
return "float"
}

Generally, all inputs per your example will return a string careless of what they entered or intended to enter. We could however build a few logics to check if what they entered is; Strings (Alphabets only) or an integer (numbers only) or any other ones per a few other logics you could base your checks on.
One of the quickest ways to check if an input contains a number or not;
isNaN(input) // this returns true if the variable does NOT contain a valid number
eg.
isNaN(123) // false
isNaN('123') // false
isNaN('1e10000') // false (This translates to Infinity, which is a number)
isNaN('foo') // true
isNaN('10px') // true
you could try regex (which is not always ideal but works)
var input = "123";
if(num.match(/^-{0,1}\d+$/)){
//return true if positive or negative
}else if(num.match(/^\d+\.\d+$/)){
//return true if float
}else{
// return false neither worked
}
You could also use the (typeof input) but this will be more convenient if your user is going to enter an expected set of entries
var input = true;
alert(typeof input);
// This eg will return bolean
Let me know if this helps.

How to tell if "123#231.23" is not a number in javascript?

parseInt("123#231.23") returns 123, which is a number.
There are tons of functions out there to detect if something is a number or not already, but they all depend on parseInt.
What is another generic way of detecting that this is not an integer without using regex?

if (isNaN("123#231.23"))
{
alert("IsNaN - not a number");
}
else
{
alert ("it is a number");
}
I'm assuming that OP need to distinguish if input is a number or not. If input is float or integer looks irrelevant to his problem.
Maybe, I'm wrong...
EDIT:
Alright, to keep everyone happy, integer in javasript is pretty big.
How big integer is in javascript check here.
Asking if something is integer is asking is it a whole number between 9007199254740992 and -9007199254740992. Wholeness of the number you may check using modulus %
$("#cmd").click(function (e) { ChectIfInteger( $("#txt").val() ) });
function ChectIfInteger(myval){
if (isNaN(myval)){
alert("not integer (not number)")
}
else{
//it is a number but it is integer?
if( myval % 1 == 0 ){
if (myval <= 9007199254740992 && myval >= -9007199254740992)
{
alert("it is integer in javascript");
}
else{
alert ("not integer");
}
}
else{
alert("nope, not integer");
}
}
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input type="text" id="txt"/>
<input type="button" id="cmd" value="test input">

Convert back to String and compare:
String(parseInt("123"))=="123" // true
String(parseInt("123.sdfs"))=="123.sdfs" //false

If you really want to check "for valid integer" you must combine isNaN with something else like this:
function isValidInteger(numberToTest) {
return !(isNaN(numberToTest) || String(parseInt(numberToTest)) !== numberToTest.toString());
}
This will evaluate like:
console.log(isValidInteger('123#231.23')); // false
console.log(isValidInteger('123231.23')); // false
console.log(isValidInteger('12323')); // true
console.log(isValidInteger(1e-1)); // false
console.log(isValidInteger('1e-1')); // false
And this work even with numbers.
Here is PLNKR to test.

I think this is the best way to test for integers:
function isInt(str) {
if (typeof str !== 'number' && typeof str !== 'string') {
return false;
}
return str % 1 === 0;
}
Just note that strings / numbers like "123.0" evaluates to true.

Here's yet another one that doesn't rely on string stuff:
function looksLikeInteger(n) {
return +n == n && +n === ~~n;
}
Probably should be called "looksLikeJavaScriptInteger" because it only works for 32-bit integers. It coerces to numeric with unary + and then checks for equality (so ugly strings and objects are tossed out there) and then checks to make sure that the numeric value doesn't change when coerced to an integer.

Javascript: Ensure Input is Numbers Only

I have a unit conversion script; my HTML contains radio buttons (to pick the units), an input field, an output field and a button.
Here's a sample of my Javascript file:
[...]
window.addEventListener("load", function(){
document.getElementById("convert").addEventListener("click", function(){
var initial = document.getElementById("initial").value;
document.getElementById("answer").innerHTML = convertObj.converted(initial);
});
[...]
});
function ConvertClass(){}
ConvertClass.prototype.converted = function(initialAmount){
if(document.getElementById("kilograms").checked) {
this.calculation = this.multiply(initialAmount, 2.2046);
} else if(document.getElementById("pounds").checked) {
this.calculation = this.divide(initialAmount, 2.2046);
}
return this.calculation.toFixed(2);
}
[...]
var convertObj = new ConvertClass();
I would like to add something that ensures a) an empty input field isn't considered a "0", and b) something other than a number doesn't display "NaN" as the answer. In both cases, I'd simply like my output to return nothing (blank). I don't want it to do nothing, in case the user submits a blank field or an invalid value after a correct number submission (which I think would result in the previous answer still being displayed.)
How do I write that? I'm assuming I should use conditions, but I don't know which ones. I did a bit of research and apparently using isNaN() isn't entirely accurate, at least not in this context.
Where do I put the code, in the function triggered by the page load or the one triggered by the button?
I'm still learning so, if possible, I'd really appreciate explanations along with the edited code. Thank you!

Inside ConvertClass.prototype.converted at the beginning of the function, add:
// this coerces it to a number instead of a string
// or NaN if it can't convert to a number
initialAmount = initialAmount.length > 0 ? +initialAmount : 0/0;
// if not a number, return empty string
if (isNaN(initialAmount)) {
return "";
}
If the input is an empty string 0/0 evaluates to NaN.

Add the following function to check whether a value in Integer.
function isInt(value) {
return !isNaN(value) &&
parseInt(Number(value)) == value &&
!isNaN(parseInt(value, 10));
}
Change your load function like this:
window.addEventListener("load", function(){
document.getElementById("convert").addEventListener("click", function(){
var initial = document.getElementById("initial").value;
if(isInt(initial)){
document.getElementById("answer").innerHTML = convertObj.converted(initial);
}else{
document.getElementById("answer").innerHTML = '';
}
});
This will make sure that when a valid integer is supplied then only it will convert otherwise answer remain empty.
For further reading on how to check integer check this:
How to check if a variable is an integer in JavaScript?
Edit: setting answer to empty string when number not integer.

how to check input value has only numbers in angular?

I want to compare a value of a field centerCode which is entered by a user into an input field. Then I want to check if it is a number and show the appropriate alert accordingly. I am not able to compare the value or variable number with the variable code .
var numbers =/^[0-9]+$/;
var code = $scope.Nuser.centerCode;
alert(code);
if(code.val(numbers))
{
alert(code.val(numbers));
}
else
{
alert("enter numbers only");
}

You're along the right lines. Numbers needs to be a Regex though, and you need to use the test function to check the input against it. The test function will return true if the string is all numbers, or false if there is anything else in it.
var numbers = new RegExp(/^[0-9]+$/);
var code = $scope.Nuser.centerCode;
if(numbers.test(code))
{
alert('code is numbers');
}
else
{
alert("enter numbers only");
}

I would suggest you to use ng-pattern instead . Something like following :
<input type="text" ng-pattern="/^[0-9]{1,7}$/" ng-model="inputNumber"/>
It will only allow the user to enter the number.
You can use angular.isNumber to check if the entered value is a number or not. Try something like the following :
if(angular.isNumber($scope.Nuser.centerCode)){
alert('Center Code is a number');
}else {
alert('Center Code is not a number');
}
Hope this will do the trick.

You can simply convert string to number and test is it's NaN (Not a Number)
isNaN(+$scope.Nuser.centerCode)
if it's false it means your centerCode contain only numbers

try this hope this is what you are looking for
if(angular.isNumber(value))
{
//your code here
}

Javascript regex to validate GPS coordinates

I have a form where a user inserts the GPS coordinates of a location to a corresponding photo. Its easy enough to filter out invalid numbers, since I just have to test for a range of (-90, 90), (-180, 180) for lat/long coordinates.
However, this also means that regular text is valid input.
I've tried changing the test pattern to
var pattern= "^[a-zA-Z]"
and is used in the function to detect alphabetical characters
$(".lat").keyup(function(){
var thisID= this.id;
var num = thisID.substring(3, thisID.length);
var thisVal = $(this).val();
//if invalid input, show error message and hide save button
if (pattern.test(thisVal)){
$("#latError"+num).fadeIn(250);
$("#save"+num).fadeOut(100)
}
else { //otherwise, hide error message and show save
$("#save"+num).fadeIn(250);
$("#latError"+num).fadeOut(100);
}
});
However, this doesn't work as Firebug complains that pattern.test is not a function What would solve this issue?

This is what i use in my project:
const regexLat = /^(-?[1-8]?\d(?:\.\d{1,18})?|90(?:\.0{1,18})?)$/;
const regexLon = /^(-?(?:1[0-7]|[1-9])?\d(?:\.\d{1,18})?|180(?:\.0{1,18})?)$/;
function check_lat_lon(lat, lon) {
let validLat = regexLat.test(lat);
let validLon = regexLon.test(lon);
return validLat && validLon;
}
check_lat_lon(-34.11242, -58.11547) Will return TRUE if valid, else FALSE
I hope this will be usefull to you!

Do you need to use regex? Consider the following:
var val = parseFloat(lat);
if (!isNaN(val) && val <= 90 && val >= -90)
return true;
else
return false;

How about the pattern -?[0-9]{1,3}[.][0-9]+ then you parseInt and check the range as you said before.

test() is a method of the RegExp object - you're running it on a string, so will fail.
Enclose your pattern in a RegExp literal (/pattern/), so
var pattern= /^[a-zA-Z]/
That will get rid of the errors you're getting, but you have a separate issue with regards to a) whether your pattern is correct for what you want it to do; b) whether you need REGEX at all.
REGEX acts on strings - it cannot be used to determine whether a number is within a given range (unless that range is 0-10 inclusive).
#flem's answer shows the best way to approach what you're doing - no REGEX needed. The call to parseInt() will catch non-numeric characters since it will return NaN if the value contains any.

#paul flemming gave a great answer, this answer extends his and includes longitude and uses typescript.
I would suggest this in place of regex for speed and simplicity.
Since, parseFloat takes a string and returns a number isNaN check isn't needed. This function allows a string or a number and converts it to string for parseFloat and will then do the simple threshold tests against +-90 & +-180.
function isValidLatAndLong(lat: number |string, lon:number|string){
const num1 = "" +lat; //convert toString
const num2 = "" +lon;
if (parseFloat(num1) <= 90 && parseFloat(num1) >= -90 && parseFloat(num2) <= 180 && parseFloat(num2) >= -180){
return true;
}
else{
return false;
}
}