how to check for datatype in node js- specifically for integer

Question

I tried the following to check for the datatype  specifically for integer   but not working   var i    5    if Number i     NaN      console log  This is not number

User · Answer

Your logic is correct but you have 2 mistakes apparently everyone missed:

just change if(Number(i) = 'NaN') to if(Number(i) == NaN)

NaN is a constant and you should use double equality signs to compare, a single one is used to assign values to variables.

User · Answer

I just made some tests in node js v4 2 4  but this is true in any javascript implementation     gt  typeof NaN  number   gt  isNaN NaN  true  gt  isNaN  hello   true   the surprise is the first one as type of NaN is  number   but that is how it is defined in javascript   So the next test brings up unexpected result   gt  typeof Number  hello    number    because Number  hello   is NaN  The following function makes results as expected   function isNumeric n     return  typeof n     number   amp  amp   isNaN n

User · Answer

You can check your numbers by checking their constructor   var i    5    if  i constructor     Number      console log  This is not number

User · Answer

I think of two ways to test for the type of a value   Method 1   You can use the isNaN javascript method  which determines if a value is NaN or not  But because in your case you are testing a numerical value converted to string  Javascript is trying to guess the type of the value and converts it to the number 5 which is not NaN  That s why if you console log out the result  you will be surprised that the code   if  isNaN i         console log  This is not number        will not return anything  For this reason a better alternative would be the method 2   Method 2   You may use javascript typeof method to test the type of a variable or value  if  typeof i     number         console log  This is not number        Notice that i m using double equal operator  because in this case the type of the value is a string but Javascript internally will convert to Number   A more robust method to force the value to numerical type is to use Number isNaN which is part of new Ecmascript 6  Harmony  proposal  hence not widespread and fully supported by different vendors

User · Answer

If you want to know if  1  ou 1 can be casted to a number  you can use this code     if  isNaN i 1          console log  i is not a number

User · Answer

i have used it in this way and its working fine   quantity prompt  Please enter the quantity   1    quantity parseInt quantity   if   isNaN  quantity          totalAmount itemPrice quantity     return totalAmount

User · Answer

you can try this one isNaN Number x   where x is any thing like string or number

User · Answer

x000D   x000D  var val         the value you want to check x000D  if Number isNaN Number val     x000D    console log  This is NOT a number     x000D   else  x000D    console log  This IS a number     x000D    x000D   x000D   x000D

[javascript] how to check for datatype in node js- specifically for integer

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