How do I check for null values in JavaScript

Question

How can I check for null values in JavaScript  I wrote the code below but it didn t work   if  pass    null    cpass    null    email    null    cemail    null    user    null               alert  fill all columns        return false            And how can I find errors in my JavaScript programs

User · Answer

I found a another way to test if the value is null:

if(variable >= 0 && typeof variable === "object")

null acts as a number and object at the same time. Comparing null >= 0 or null <= 0 results in true. Comparing null === 0 or null > 0 or null < 0 will result in false. But as null is also an object we can detect it as a null.

I made a more complex function natureof witch will do better than typeof and can be told what types to include or keep grouped

_x000D_

/* function natureof(variable, [included types])_x000D_
included types are _x000D_
    null - null will result in "undefined" or if included, will result in "null"_x000D_
    NaN - NaN will result in "undefined" or if included, will result in "NaN"_x000D_
    -infinity - will separate negative -Inifity from "Infinity"_x000D_
    number - will split number into "int" or "double"_x000D_
    array - will separate "array" from "object"_x000D_
    empty - empty "string" will result in "empty" or_x000D_
    empty=undefined - empty "string" will result in "undefined"_x000D_
*/_x000D_
function natureof(v, ...types){_x000D_
/*null*/            if(v === null) return types.includes('null') ? "null" : "undefined";_x000D_
/*NaN*/             if(typeof v == "number") return (isNaN(v)) ? types.includes('NaN') ? "NaN" : "undefined" : _x000D_
/*-infinity*/       (v+1 === v) ? (types.includes('-infinity') && v === Number.NEGATIVE_INFINITY) ? "-infinity" : "infinity" : _x000D_
/*number*/          (types.includes('number')) ? (Number.isInteger(v)) ? "int" : "double" : "number";_x000D_
/*array*/           if(typeof v == "object") return (types.includes('array') && Array.isArray(v)) ? "array" : "object";_x000D_
/*empty*/           if(typeof v == "string") return (v == "") ? types.includes('empty') ? "empty" : _x000D_
/*empty=undefined*/ types.includes('empty=undefined') ? "undefined" : "string" : "string";_x000D_
                    else return typeof v_x000D_
}_x000D_
_x000D_
// DEMO_x000D_
let types = [null, "", "string", undefined, NaN, Infinity, -Infinity, false, "false", true, "true", 0, 1, -1, 0.1, "test", {var:1}, [1,2], {0: 1, 1: 2, length: 2}]_x000D_
_x000D_
for(i in types){_x000D_
console.log("natureof ", types[i], " = ", natureof(types[i], "null", "NaN", "-infinity", "number", "array", "empty=undefined")) _x000D_
}

_x000D_

User · Answer

Strict equality operator -  We can check null by       if   value     null         Just by using if  if  value          will evaluate to true if value is not    null undefined NaN empty string      false  0

User · Answer

Firstly  you have a return statement without a function body  Chances are that that will throw an error   A cleaner way to do your check would be to simply use the   operator   if   pass     cpass     email     cemail     user         alert  fill all columns

User · Answer

Try this   if   variable  amp  amp  typeof variable      object            variable is null

User · Answer

Actually I think you may need to use if  value     null    value     undefined  because if you use if  value  you may also filter 0 or false values   Consider these two functions   const firstTest   value   gt        if  value            console log  passed          else           console log  failed            const secondTest   value   gt        if  value     null  amp  amp  value     undefined            console log  passed          else           console log  failed             firstTest 0                 result  failed secondTest 0                result  passed  firstTest false             result  failed secondTest false            result  passed  firstTest                   result  failed secondTest                  result  passed  firstTest null              result  failed secondTest null             result  failed  firstTest undefined         result  failed secondTest undefined        result  failed   In my situation  I just needed to check if the value is null and undefined and I did not want to filter 0 or false or    values  so I used the second test  but you may need to filter them too which may cause you to use first test

User · Answer

Improvement over the accepted answer by explicitly checking for null but with a simplified syntax   if   pass  cpass  email  cemail  user  every x  gt x   null            your code here          x000D   x000D     Test x000D  let pass 1  cpass 1  email 1  cemail 1  user 1     just to test x000D   x000D  if   pass  cpass  email  cemail  user  every x  gt x   null     x000D         your code here     x000D      console log   Yayy  None of them are null    x000D    else   x000D      console log   Oops  At-lease one of them is null    x000D    x000D   x000D   x000D

User · Answer

This is a comment on WebWanderer s solution regarding checking for NaN  I don t have enough rep yet to leave a formal comment    The solution reads as   if  parseInt variable   amp  amp  variable    0  amp  amp  typeof variable      number     but this will fail for rational numbers which would round to 0  such as variable   0 1   A better test would be   if isNaN variable   amp  amp  typeof variable      number

User · Answer

to check for undefined and null in javascript you need just to write the following    if   var            console log  var IS null or undefined      else           console log  var is NOT null or undefined

User · Answer

At first sight  it looks like a simple trade-off between coverage and strictness      covers multiple values  can handle more scenarios in less code      is the most strict  and that makes it predictable   Predictability always wins  and that appears to make     a one-fits-all solution   But it is wrong  Even though     is predictable  it does not always result in predictable code  because it overlooks scenarios  const options        if  options callback     null      options callback            error -- gt  callback is undefined     In general    does a more predictable job for null checks   In general  null and undefined both mean the same thing   quot something s missing quot   For predictability  you need to check both values  And then    null does a perfect job  because it covers exactly those 2 values   i e     null is equivalent to     null  amp  amp      undefined   In exceptional cases you do want a clear distinction between null and undefined  And in those cases you re better of with a strict     undefined or     null   e g  a distinction between missing ignore skip and empty clear remove   But it is rare    It is not only rare  it s something to avoid  You can t store undefined in a traditional database  And you shouldn t rely on undefined values in your API designs neither  due to interopability reasons  But even when you don t make a distinction at all  you can t assume that undefined won t happen  People all around us indirectly take actions that generalize null undefined  which is why questions like this are closed as  quot opinionated quot     So  to get back to your question  There s nothing wrong with using    null  It does exactly what it should do     FIX 1 -- gt  yes     is very explicit const options        if  options callback     null  amp  amp       options callback     undefined      options callback           FIX 2 -- gt  but    is more accurate here const options        if  options callback    null      options callback

User · Answer

Checking error conditions      Typical API response data let data       status  true    user        total  0    activity   sports  1        A flag that checks whether all conditions were met or not var passed   true      Boolean check if  data  status       undefined    data  status      false     console log  Undefined   no  status  data      passed   false        Array dict check if  data  user       undefined     data  user   length     console log  Undefined   no  user  data      passed   false        Checking a key in a dictionary if  data  activity       undefined    data  activity    time       undefined      console log  Undefined   no  time  data       passed   false        Other values check if  data  total       undefined     data  total       console log  Undefined   no  total  data      passed   false        Passed all tests  if  passed     console log  Passed all tests

User · Answer

I made this very simple function that works wonders   function safeOrZero route      try       Function  return    route            catch  error        return 0        return Function  return    route            The route is whatever chain of values that can blow up  I use it for jQuery cheerio and objects and such   Examples 1  a simple object such as this const testObj    items     val   haya       val  null      val   hum           But it could be a very large object that we haven t even made  So I pass it through   let value1   testobj items 2  val       hum   let value2   testobj items 3  val      Uncaught TypeError  Cannot read property  val  of undefined  let svalue1   safeOrZero  testobj items 2  val        hum   let svalue2   safeOrZero  testobj items 3  val       0   Of course if you prefer you can use null or  No value     Whatever suit your needs   Usually a DOM query or a jQuery selector may throw an error if it s not found  But using something like   const bookLink   safeOrZero    span guidebook  gt  a   0  href   if bookLink

User · Answer

just replace the    with     in all places      is a loose or abstract equality comparison      is a strict equality comparison  See the MDN article on Equality comparisons and sameness for more detail

User · Answer

You can check if some value is null as follows  pass cpass email cemail user  some x  gt  x   null     x000D   x000D  let pass 1  let cpass 2  let email 3  let cemail null  let user 5   if    pass cpass email cemail user  some x  gt  x   null               alert  fill all columns          return false         x000D   x000D   x000D   BONUS  Why     is more clear than     source  a    b  a     b

User · Answer

You can use lodash module to check value is null or undefined    isNil value  Example    country   Abc        isNil country        false     state  null       isNil state        true  city  undefined       isNil state        true     pin  true       isNil pin         false      Reference link  https   lodash com docs  isNil

User · Answer

To check for null SPECIFICALLY you would use this   if  variable     null    This test will ONLY pass for null and will not pass for     undefined  false  0  or NaN   Additionally  I ve provided absolute checks for each  false-like  value  one that would return true for  variable    Note  for some of the absolute checks  you will need to implement use of the absolutely equals      and typeof   I ve created a JSFiddle here to show all of the individual tests working  Here is the output of each check   Null Test   if  variable     null   - variable        false  typeof variable   string  - variable   null   true  typeof variable   object  - variable   undefined   false  typeof variable   undefined  - variable   false   false  typeof variable   boolean  - variable   0   false  typeof variable   number  - variable   NaN   false  typeof variable   number    Empty String Test   if  variable          - variable        true  typeof variable   string  - variable   null   false  typeof variable   object  - variable   undefined   false  typeof variable   undefined  - variable   false   false  typeof variable   boolean  - variable   0   false  typeof variable   number  - variable   NaN   false  typeof variable   number     Undefined Test   if  typeof variable     undefined    -- or --  if  variable     undefined   - variable        false  typeof variable   string  - variable   null   false  typeof variable   object  - variable   undefined   true  typeof variable   undefined  - variable   false   false  typeof variable   boolean  - variable   0   false  typeof variable   number  - variable   NaN   false  typeof variable   number    False Test   if  variable     false   - variable        false  typeof variable   string  - variable   null   false  typeof variable   object  - variable   undefined   false  typeof variable   undefined  - variable   false   true  typeof variable   boolean  - variable   0   false  typeof variable   number  - variable   NaN   false  typeof variable   number    Zero Test   if  variable     0   - variable        false  typeof variable   string  - variable   null   false  typeof variable   object  - variable   undefined   false  typeof variable   undefined  - variable   false   false  typeof variable   boolean  - variable   0   true  typeof variable   number  - variable   NaN   false  typeof variable   number    NaN Test   if  typeof variable     number   amp  amp   parseFloat variable   amp  amp  variable     0   -- or --  if  isNaN variable    - variable        false  typeof variable   string  - variable   null   false  typeof variable   object  - variable   undefined   false  typeof variable   undefined  - variable   false   false  typeof variable   boolean  - variable   0   false  typeof variable   number  - variable   NaN   true  typeof variable   number   As you can see  it s a little more difficult to test against NaN

User · Answer

you can use try catch finally   try        document getElementById  mydiv   innerHTML    Success    assuming  mydiv  is undefined    catch  e          if  e name toString       TypeError     evals to true in this case        do something     finally         you can also throw your own errors  See this

User · Answer

In JavaScript  no string is equal to null   Maybe you expected pass    null to be true when pass is an empty string because you re aware that the loose equality operator    performs certain kinds of type coercion   For example  this expression is true         0   In contrast  the strict equality operator     says that this is false          0   Given that    and 0 are loosely equal  you might reasonably conjecture that    and null are loosely equal  However  they are not   This expression is false         null   The result of comparing any string to null is false  Therefore  pass    null and all your other tests are always false  and the user never gets the alert   To fix your code  compare each value to the empty string   pass          If you re certain that pass is a string  pass       will also work because only an empty string is loosely equal to the empty string  On the other hand  some experts say that it s a good practice to always use strict equality in JavaScript unless you specifically want to do the type coercion that the loose equality operator performs   If you want to know what pairs of values are loosely equal  see the table  Sameness comparisons  in the Mozilla article on this topic

User · Answer

This will not work in case of Boolean values coming from DB for ex    value   false   if  value          it will change all false values to not available    return  not available

User · Answer

Javascript is very flexible with regards to checking for  null  values   I m guessing you re actually looking for empty strings  in which case this simpler code will work   if  pass     cpass     email     cemail     user     Which will check for empty strings       null  undefined  false and the numbers 0 and NaN  Please note that if you are specifically checking for numbers it is a common mistake to miss 0 with this method  and num     0 is preferred  or num     -1 or  num  hacky code that also checks against -1   for functions that return -1  e g  indexOf

User · Answer

AFAIK in JAVASCRIPT when a variable is declared but has not assigned value  its type is undefined  so we can check variable even if it would be an object holding some instance in place of value   create a helper method for checking nullity that returns true and use it in your API   helper function to check if variable is empty   function isEmpty item       if item           return false       else          return true            try-catch exceptional API call   try        var pass  cpass  email  cemail  user     only declared but contains nothing          parametrs checking     if isEmpty pass     isEmpty cpass     isEmpty email     isEmpty cemail     isEmpty user            console log  One or More of these parameter contains no vlaue   pass  and-or  cpass  and-or  email  and-or  cemail  and-or  user          else             do stuff          catch  e        if  e instanceof ReferenceError            console log e message      debugging purpose         return true        else           console log e message      debugging purpose         return true            some test cases   var item          isEmpty  true var item           isEmpty  false var item     isEmpty  true var item   0     isEmpty  true var item   1     isEmpty  false var item    AAAAA      isEmpty  false var item   NaN     isEmpty  true var item   null     isEmpty  true var item   undefined     isEmpty  true  console log  isEmpty    isEmpty item

[javascript] How do I check for null values in JavaScript?

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