Check if input is number or letter javascript

Question

I m using forms in HTML and javascript  I would like an alert to pop up only if the user inputs a LETTER and clicks submit   So I have the HTML code    lt form name  myForm  action    onsubmit  return checkInp    method  post  gt      First name   lt input type  text  name  age  gt   lt input type  submit  value  Submit  gt       And the javascript code   function checkInp     var x document forms  myForm    age   value  if  x consists of any letters     this is the code I need to change   alert  Must input numbers    return false

User · Answer

You could use the isNaN  Function  It returns true if the data is not a number  That would be something like that   function checkInp         var x document forms  myForm    age   value      if  isNaN x      this is the code I need to change               alert  Must input numbers            return false            Note  isNan considers 10 2 as a valid number

User · Answer

you can use isNaN    it returns true when data is not number   var data    hello there   if isNaN data      alert  it is not number     else     alert  its a valid number

User · Answer

I know this post is old but it was the first one that popped up when I did a search  I tried  Kim Kling RegExp but it failed miserably  Also prior to finding this forum I had tried almost all the other variations listed here  In the end  none of them worked except this one I created  it works fine  plus it is es6      const regex   new RegExp    0-9     g        const val   document forms  quot myForm quot    quot age quot   value       if  val match regex            alert  quot Must be a valid number quot

User · Answer

I think the easiest would be to create a Number object with the string and check if with the help of isInteger function provided by Number class itself   Number isInteger Number  1      true Number isInteger Number  1 mango      false Number isInteger Number 1     true Number isInteger Number 1 9     false

User · Answer

Use Regular Expression to match for only letters  It s also good to have knowledge about  if you ever need to do something more complicated  like make sure it s a certain count of numbers   function checkInp         var x document forms  myForm    age   value      var regex    a-zA-Z          if   x match regex                 alert  Must input string            return false            Even better would be to deny anything but numbers   function checkInp         var x document forms  myForm    age   value      var regex    0-9          if  x match regex                 alert  Must input numbers            return false

User · Answer

Just find the remainder by dividing by 1  that is x 1  If the remainder is 0  it means that x is a whole number  Otherwise  you have to display the message  Must input numbers   This will work even in the case of strings  decimal numbers etc   function checkInp         var x   document forms  myForm    age   value      if   x 1     0                 alert  Must input numbers            return false

User · Answer

The best and modern way is typeof  variable  if you care about real number not number from string  For example   var a   1  var b    1    typeof a     Output   number  typeof b     Output   string

User · Answer

A better error-free  code would be like   function isReallyNumber data        return typeof data      number   amp  amp   isNaN data       This will handle empty strings as well  Another reason  isNaN  12   equals to false but  12  is a string and not a number  so it should result to true  Lastly  a bonus link which might interest you

User · Answer

You can use the isNaN function to determine if a value does not convert to a number  Example as below   function checkInp       var x document forms  myForm    age   value    if  isNaN x            alert  Must input numbers        return false

User · Answer

Thanks  I used  str8up7od answer to create a function today which also checks if the input is empty      function is number input            if input                     return false          let regex   new RegExp    0-9     g            return  input match regex      null

User · Answer

Try this   if parseInt  0  x  10   gt  0     x is integer

[javascript] Check if input is number or letter javascript

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