type checking in javascript

Question

How can I check if a variable is currently an integer type   I ve looked for some sort of resource for this and I think the     operator is important  but I m not sure how to check if a variable is an Integer  or an Array for that matter

User · Answer

Try this code    alert typeof 1      number

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You may also have a look on Runtyper - a tool that performs type checking of operands in      and other operations   For your example  if you have strict comparison x     y and x   123  y    123   it will automatically check typeof x  typeof y and show warning in console      Strict compare of different types  123  number       123   string

User · Answer

I know you re interested in Integer numbers so I won t re answer that but if you ever wanted to check for Floating Point numbers you could do this    function isFloat  x         return   typeof x      number   amp  amp  Math abs  x   1    gt  0       Note  This MAY treat numbers ending in  0  or any logically equivalent number of 0 s  as an INTEGER  It actually needs a floating point precision error to occur to detect the floating point values in that case   Ex   alert isFloat 5 2        returns true alert isFloat 5          returns false alert isFloat 5 0        return could be either true or false

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A number is an integer if its modulo  1 is 0-  function isInt n       return  typeof n    number   amp  amp  n 1   0       This is only as good as javascript gets- say  - ten to the 15th    isInt Math pow 2 50   1  returns true  as does Math pow 2 50   1    Math pow 2 50

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Quite a few utility libraries such as YourJS offer functions for determining if something is an array or if something is an integer or a lot of other types as well   YourJS defines isInt by checking if the value is a number and then if it is divisible by 1   function isInt x      return typeOf x   Number    amp  amp  x   1    0      The above snippet was taken from this YourJS snippet and thusly only works because typeOf is defined by the library   You can download a minimalistic version of YourJS which mainly only has type checking functions such as typeOf    isInt   and isArray     http   yourjs com snippets build 34 2

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A variable will never be an integer type in JavaScript     it doesn t distinguish between different types of Number   You can test if the variable contains a number  and if that number is an integer     typeof foo      number    amp  amp  Math floor foo      foo   If the variable might be a string containing an integer and you want to see if that is the case    foo    parseInt foo  10

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These days  ECMAScript 6  ECMA-262  is  in the house   Use Number isInteger x  to ask the question you want to ask with respect to the type of x   js gt  var x   3 js gt  Number isInteger x  true js gt  var y   3 1 js gt  Number isInteger y  false

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A clean approach You can consider using a very small  dependency-free library like Not  Solves all problems     at the basic level it supports primitives let number   10 let array      not  number   10     returns false not  number          throws error     so you need to define your own  let not   Object create Not   not defineType       primitive   number       type   integer       pass  function candidate               pre-ECMA6         return candidate toFixed 0      candidate toString              ECMA6         return Number isInteger candidate           not not  integer   4 4     gives error message not is  integer   4 4     returns false not is  integer   8     returns true  If you make it a habit  your code will be much stronger  Typescript solves part of the problem but doesn t work at runtime  which is also important  function test  string  boolean           any of these below will throw errors to protect you     not  string   string      not  boolean   boolean          continue with your code

[javascript] type checking in javascript

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