How do I check for an empty/undefined/null string in JavaScript?

Question

Is there a string.Empty in JavaScript, or is it just a case of checking for ""?

Answer 1

Empty string, undefined, null, ...

To check for a truthy value:

if (strValue) {
    // strValue was non-empty string, true, 42, Infinity, [], ...
}

To check for a falsy value:

if (!strValue) {
    // strValue was empty string, false, 0, null, undefined, ...
}

---

Empty string (only!)

To check for exactly an empty string, compare for strict equality against "" using the === operator:

if (strValue === "") {
    // strValue was empty string
}

To check for not an empty string strictly, use the !== operator:

if (strValue !== "") {
    // strValue was not an empty string
}

Answer 2

The Underscore.js JavaScript library, http://underscorejs.org/, provides a very useful _.isEmpty() function for checking for empty strings and other empty objects.

Reference: http://underscorejs.org/#isEmpty

isEmpty _.isEmpty(object)
Returns true if an enumerable object contains no values (no enumerable own-properties). For strings and array-like objects _.isEmpty checks if the length property is 0.

_.isEmpty([1, 2, 3]);
=> false

_.isEmpty({});
=> true

Other very useful Underscore.js functions include:

• http://underscorejs.org/#isNull _.isNull(object)
• http://underscorejs.org/#isUndefined
• _.isUndefined(value)
• http://underscorejs.org/#has _.has(object, key)

Answer 3

Trimming whitespace with the null-coalescing operator:

if (!str?.trim()) {
  // do something...
}

Answer 4

I usually use something like this,

if (!str.length) {
    // Do something
}

Answer 5

I have not noticed an answer that takes into account the possibility of null characters in a string. For example, if we have a null character string:

var y = "\0"; // an empty string, but has a null character
(y === "") // false, testing against an empty string does not work
(y.length === 0) // false
(y) // true, this is also not expected
(y.match(/^[\s]*$/)) // false, again not wanted

To test its nullness one could do something like this:

String.prototype.isNull = function(){ 
  return Boolean(this.match(/^[\0]*$/)); 
}
...
"\0".isNull() // true

It works on a null string, and on an empty string and it is accessible for all strings. In addition, it could be expanded to contain other JavaScript empty or whitespace characters (i.e. nonbreaking space, byte order mark, line/paragraph separator, etc.).

Answer 6

You can able to validate following ways and understand the difference.

var j = undefined;
console.log((typeof j == 'undefined') ? "true":"false");
var j = null; 
console.log((j == null) ? "true":"false");
var j = "";
console.log((!j) ? "true":"false");
var j = "Hi";
console.log((!j) ? "true":"false");

Answer 7

Check if it's type string AND if it's not empty:

const isNonEmptyString = (val) => typeof val === 'string' && !!val

Answer 8

function tell()
{
    var pass = document.getElementById('pasword').value;
    var plen = pass.length;

    // Now you can check if your string is empty as like
    if(plen==0)
    {
        alert('empty');
    }
    else
    {
        alert('you entered something');
    }
}

<input type='text' id='pasword' />

This is also a generic way to check if field is empty.

Answer 9

Don't assume that the variable you check is a string. Don't assume that if this var has a length, then it's a string.

The thing is: think carefully about what your app must do and can accept. Build something robust.

If your method / function should only process a non empty string then test if the argument is a non empty string and don't do some 'trick'.

As an example of something that will explode if you follow some advices here not carefully.

var getLastChar = function (str) {
 if (str.length > 0)
   return str.charAt(str.length - 1)
}

getLastChar('hello')
=> "o"

getLastChar([0,1,2,3])
=> TypeError: Object [object Array] has no method 'charAt'

So, I'd stick with

if (myVar === '')
  ...

Answer 10

Performance

I perform tests on macOS v10.13.6 (High Sierra) for 18 chosen solutions. Solutions works slightly different (for corner-case input data) which was presented in the snippet below.

Conclusions

• the simple solutions based on !str,==,=== and length are fast for all browsers (A,B,C,G,I,J)
• the solutions based on the regular expression (test,replace) and charAt are slowest for all browsers (H,L,M,P)
• the solutions marked as fastest was fastest only for one test run - but in many runs it changes inside 'fast' solutions group

Details

In the below snippet I compare results of chosen 18 methods by use different input parameters

• "" "a" " "- empty string, string with letter and string with space
• [] {} f- array, object and function
• 0 1 NaN Infinity - numbers
• true false - Boolean
• null undefined

Not all tested methods support all input cases.

function A(str) {
  let r=1;
  if (!str)
    r=0;
  return r;
}

function B(str) {
  let r=1;
  if (str == "")
    r=0;
  return r;
}

function C(str) {
  let r=1;
  if (str === "")
    r=0;
  return r;
}

function D(str) {
  let r=1;
  if(!str || 0 === str.length)
    r=0;
  return r;
}

function E(str) {
  let r=1;
  if(!str || /^\s*$/.test(str))
    r=0;
  return r;
}

function F(str) {
  let r=1;
  if(!Boolean(str))
    r=0;
  return r;
}

function G(str) {
  let r=1;
  if(! ((typeof str != 'undefined') && str) )
    r=0;
  return r;
}

function H(str) {
  let r=1;
  if(!/\S/.test(str))
    r=0;
  return r;
}

function I(str) {
  let r=1;
  if (!str.length)
    r=0;
  return r;
}

function J(str) {
  let r=1;
  if(str.length <= 0)
    r=0;
  return r;
}

function K(str) {
  let r=1;
  if(str.length === 0 || !str.trim())
    r=0;
  return r;
}

function L(str) {
  let r=1;
  if ( str.replace(/\s/g,"") == "")
    r=0;
  return r;
}

function M(str) {
  let r=1;
  if((/^\s*$/).test(str))
    r=0;
  return r;
}


function N(str) {
  let r=1;
  if(!str || !str.trim().length)
    r=0;
  return r;
}

function O(str) {
  let r=1;
  if(!str || !str.trim())
    r=0;
  return r;
}

function P(str) {
  let r=1;
  if(!str.charAt(0))
    r=0;
  return r;
}

function Q(str) {
  let r=1;
  if(!str || (str.trim()==''))
    r=0;
  return r;
}

function R(str) {
  let r=1;
  if (typeof str == 'undefined' ||
      !str ||
      str.length === 0 ||
      str === "" ||
      !/[^\s]/.test(str) ||
      /^\s*$/.test(str) ||
      str.replace(/\s/g,"") === "")

    r=0;
  return r;
}




// --- TEST ---

console.log(                  '   ""  "a"  " " [] {} 0 1 NaN Infinity f true false null undefined ');
let log1 = (s,f)=> console.log(`${s}: ${f("")}   ${f("a")}    ${f(" ")}   ${f([])}  ${f({})}  ${f(0)} ${f(1)} ${f(NaN)}   ${f(Infinity)}        ${f(f)} ${f(true)}    ${f(false)}     ${f(null)}    ${f(undefined)}`);
let log2 = (s,f)=> console.log(`${s}: ${f("")}   ${f("a")}    ${f(" ")}   ${f([])}  ${f({})}  ${f(0)} ${f(1)} ${f(NaN)}   ${f(Infinity)}        ${f(f)} ${f(true)}    ${f(false)}`);
let log3 = (s,f)=> console.log(`${s}: ${f("")}   ${f("a")}    ${f(" ")}`);

log1('A', A);
log1('B', B);
log1('C', C);
log1('D', D);
log1('E', E);
log1('F', F);
log1('G', G);
log1('H', H);

log2('I', I);
log2('J', J);

log3('K', K);
log3('L', L);
log3('M', M);
log3('N', N);
log3('O', O);
log3('P', P);
log3('Q', Q);
log3('R', R);

And then for all methods I perform speed test case str = "" for browsers Chrome v78.0.0, Safari v13.0.4, and Firefox v71.0.0 - you can run tests on your machine here

Answer 11

The following regular expression is another solution, that can be used for null, empty or undefined string.

(/(null|undefined|^$)/).test(null)

I added this solution, because it can be extended further to check empty or some value like as follow. The following regular expression is checking either string can be empty null undefined or it has integers only.

(/(null|undefined|^$|^\d+$)/).test()

Answer 12

I didn't see a good answer here (at least not an answer that fits for me)

So I decided to answer myself:

value === undefined || value === null || value === "";

You need to start checking if it's undefined. Otherwise your method can explode, and then you can check if it equals null or is equal to an empty string.

You cannot have !! or only if(value) since if you check 0 it's going to give you a false answer (0 is false).

With that said, wrap it up in a method like:

public static isEmpty(value: any): boolean { return value === undefined || value === null || value === ""; }

PS.: You don't need to check typeof, since it would explode and throw even before it enters the method

Answer 13

You can easily add it to native String object in JavaScript and reuse it over and over...
Something simple like below code can do the job for you if you want to check '' empty strings:

String.prototype.isEmpty = String.prototype.isEmpty || function() {
  return !(!!this.length);
}

Otherwise if you'd like to check both '' empty string and ' ' with space, you can do that by just adding trim(), something like the code below:

String.prototype.isEmpty = String.prototype.isEmpty || function() {
   return !(!!this.trim().length);
}

and you can call it this way:

''.isEmpty(); //return true
'alireza'.isEmpty(); //return false

Answer 14

Try this code:

function isEmpty(strValue)
{
    // Test whether strValue is empty
    if (!strValue || strValue.trim() === "" ||
        (strValue.trim()).length === 0) {
        // Do something
    }
}

Answer 15

This is a falsy value.

The first solution:

const str = "";
return str || "Hello"

The second solution:

const str = "";
return (!!str) || "Hello"; // !!str is Boolean

The third solution:

const str = "";
return (+str) || "Hello"; // !!str is Boolean

Answer 16

Try:

if (str && str.trim().length) {  
    //...
}

Answer 17

The ultimate and shortest variant of the isBlank function:

/**
 * Will return:
 * False for: for all strings with chars
 * True for: false, null, undefined, 0, 0.0, "", " ".
 *
 * @param str
 * @returns {boolean}
 */
function isBlank(str){
    return (!!!str || /^\s*$/.test(str));
}

// tests
console.log("isBlank TRUE variants:");
console.log(isBlank(false));
console.log(isBlank(undefined));
console.log(isBlank(null));
console.log(isBlank(0));
console.log(isBlank(0.0));
console.log(isBlank(""));
console.log(isBlank(" "));

console.log("isBlank FALSE variants:");
console.log(isBlank("0"));
console.log(isBlank("0.0"));
console.log(isBlank(" 0"));
console.log(isBlank("0 "));
console.log(isBlank("Test string"));
console.log(isBlank("true"));
console.log(isBlank("false"));
console.log(isBlank("null"));
console.log(isBlank("undefined"));

Answer 18

All these answers are nice.

But I cannot be sure that variable is a string, doesn't contain only spaces (this is important for me), and can contain '0' (string).

My version:

function empty(str){
    return !str || !/[^\s]+/.test(str);
}

empty(null); // true
empty(0); // true
empty(7); // false
empty(""); // true
empty("0"); // false
empty("  "); // true

Sample on jsfiddle.

Answer 19

Well, the simplest function to check this is...

const checkEmpty = string => (string.trim() === "") || !string.trim();

Usage:

checkEmpty(""); // returns true.
checkEmpty("mystr"); // returns false.

It's that dead simple. :)

Answer 20

All the previous answers are good, but this will be even better. Use dual NOT operators (!!):

if (!!str) {
    // Some code here
}

Or use type casting:

if (Boolean(str)) {
    // Code here
}

Both do the same function. Typecast the variable to Boolean, where str is a variable.

• It returns false for null, undefined, 0, 000, "", false.

• It returns true for all string values other than the empty string (including strings like "0" and " ")

Answer 21

I use:

function empty(e) {
  switch (e) {
    case "":
    case 0:
    case "0":
    case null:
    case false:
    case undefined:
      return true;
    default:
      return false;
  }
}

empty(null) // true
empty(0) // true
empty(7) // false
empty("") // true
empty((function() {
    return ""
})) // false

Answer 22

For checking if a variable is falsey or if it has length attribute equal to zero (which for a string, means it is empty), I use:

function isEmpty(str) {
    return (!str || str.length === 0 );
}

_{(Note that strings aren't the only variables with a length attribute, arrays have them as well, for example.)}

Alternativaly, you can use the (not so) newly optional chaining and arrow functions to simplify:

const isEmpty = (str) => (!str?.length);

It will check the length, returning undefined in case of a nullish value, without throwing an error. In the case of an empty value, zero is falsy and the result is still valid.

For checking if a variable is falsey or if the string only contains whitespace or is empty, I use:

function isBlank(str) {
    return (!str || /^\s*$/.test(str));
}

If you want, you can monkey-patch the String prototype like this:

String.prototype.isEmpty = function() {
    // This doesn't work the same way as the isEmpty function used 
    // in the first example, it will return true for strings containing only whitespace
    return (this.length === 0 || !this.trim());
};
console.log("example".isEmpty());

_{Note that monkey-patching built-in types are controversial, as it can break code that depends on the existing structure of built-in types, for whatever reason.}

Answer 23

Try this

str.value.length == 0

Answer 24

var x ="  ";
var patt = /^\s*$/g;
isBlank = patt.test(x);
alert(isBlank); // Is it blank or not??
x = x.replace(/\s*/g, ""); // Another way of replacing blanks with ""
if (x===""){
    alert("ya it is blank")
}

Answer 25

You could also go with regular expressions:

if((/^\s*$/).test(str)) { }

Checks for strings that are either empty or filled with whitespace.

Answer 26

Very generic "All-In-One" Function (not recommended though):

function is_empty(x)
{
    return (                                                           //don't put newline after return
        (typeof x == 'undefined')
              ||
        (x == null)
              ||
        (x == false)        //same as: !x
              ||
        (x.length == 0)
              ||
        (x == 0)            // note this line, you might not need this. 
              ||
        (x == "")
              ||
        (x.replace(/\s/g,"") == "")
              ||
        (!/[^\s]/.test(x))
              ||
        (/^\s*$/.test(x))
    );
}

However, I don't recommend to use that, because your target variable should be of specific type (i.e. string, or numeric, or object?), so apply the checks that are relative to that variable.

Answer 27

Starting with:

return (!value || value == undefined || value == "" || value.length == 0);

Looking at the last condition, if value == "", its length must be 0. Therefore drop it:

return (!value || value == undefined || value == "");

But wait! In JavaScript, an empty string is false. Therefore, drop value == "":

return (!value || value == undefined);

And !undefined is true, so that check isn't needed. So we have:

return (!value);

And we don't need parentheses:

return !value

Answer 28

complete example. use Object.keys() for types string,array, and object

function isEmpty(input){
    switch(typeof input){
      case 'undefined': return true
      case 'string':
      case 'object':
         return Object.keys(input).length == 0
      case 'boolean':
      case 'bigint':
      case 'number': return input == 0
    }
}
function log(...logs){
   for(let i = 0;i < logs.length;i++){
     if(i % 2 == 1){
        console.log(logs[i - 1],'=', logs[i])
     }
   }
}
log(
   isEmpty(),      'empty undefined',   // true
   isEmpty(''),    'empty string',      // true
   isEmpty('abc'), 'empty string',      // false
   isEmpty([]),    'empty array',       // true
   isEmpty([2,3]), 'empty array',       // false
   isEmpty({}),    'empty object',      // true
   isEmpty({a: 'abc'}), 'empty object', // false
   isEmpty(false), 'empty boolean',     // true
   isEmpty(true),  'empty boolean',     // false
   isEmpty(0n),    'empty bigint',      // true
   isEmpty(2n),    'empty bigint',      // false
   isEmpty(0),     'empty number',      // true
   isEmpty(2),     'empty number'       // false
)

Answer 29

You can check this using the typeof operator along with the length method.

const isNonEmptyString = (value) => typeof(value) == 'string' && value.length > 0

Answer 30

I prefer to use not blank test instead of blank

function isNotBlank(str) {
   return (str && /^\s*$/.test(str));
}

Answer 31

Also, in case you consider a whitespace filled string as "empty".

You can test it with this regular expression:

!/\S/.test(string); // Returns true if blank.

Answer 32

I did some research on what happens if you pass a non-string and non-empty/null value to a tester function. As many know, (0 == "") is true in JavaScript, but since 0 is a value and not empty or null, you may want to test for it.

The following two functions return true only for undefined, null, empty/whitespace values and false for everything else, such as numbers, Boolean, objects, expressions, etc.

function IsNullOrEmpty(value)
{
    return (value == null || value === "");
}
function IsNullOrWhiteSpace(value)
{
    return (value == null || !/\S/.test(value));
}

More complicated examples exists, but these are simple and give consistent results. There is no need to test for undefined, since it's included in (value == null) check. You may also mimic C# behaviour by adding them to String like this:

String.IsNullOrEmpty = function (value) { ... }

You do not want to put it in Strings prototype, because if the instance of the String-class is null, it will error:

String.prototype.IsNullOrEmpty = function (value) { ... }
var myvar = null;
if (1 == 2) { myvar = "OK"; } // Could be set
myvar.IsNullOrEmpty(); // Throws error

I tested with the following value array. You can loop it through to test your functions if in doubt.

// Helper items
var MyClass = function (b) { this.a = "Hello World!"; this.b = b; };
MyClass.prototype.hello = function () { if (this.b == null) { alert(this.a); } else { alert(this.b); } };
var z;
var arr = [
// 0: Explanation for printing, 1: actual value
    ['undefined', undefined],
    ['(var) z', z],
    ['null', null],
    ['empty', ''],
    ['space', ' '],
    ['tab', '\t'],
    ['newline', '\n'],
    ['carriage return', '\r'],
    ['"\\r\\n"', '\r\n'],
    ['"\\n\\r"', '\n\r'],
    ['" \\t \\n "', ' \t \n '],
    ['" txt \\t test \\n"', ' txt \t test \n'],
    ['"txt"', "txt"],
    ['"undefined"', 'undefined'],
    ['"null"', 'null'],
    ['"0"', '0'],
    ['"1"', '1'],
    ['"1.5"', '1.5'],
    ['"1,5"', '1,5'], // Valid number in some locales, not in JavaScript
    ['comma', ','],
    ['dot', '.'],
    ['".5"', '.5'],
    ['0', 0],
    ['0.0', 0.0],
    ['1', 1],
    ['1.5', 1.5],
    ['NaN', NaN],
    ['/\S/', /\S/],
    ['true', true],
    ['false', false],
    ['function, returns true', function () { return true; } ],
    ['function, returns false', function () { return false; } ],
    ['function, returns null', function () { return null; } ],
    ['function, returns string', function () { return "test"; } ],
    ['function, returns undefined', function () { } ],
    ['MyClass', MyClass],
    ['new MyClass', new MyClass()],
    ['empty object', {}],
    ['non-empty object', { a: "a", match: "bogus", test: "bogus"}],
    ['object with toString: string', { a: "a", match: "bogus", test: "bogus", toString: function () { return "test"; } }],
    ['object with toString: null', { a: "a", match: "bogus", test: "bogus", toString: function () { return null; } }]
];

Answer 33

Ignoring whitespace strings, you could use this to check for null, empty and undefined:

var obj = {};
(!!obj.str) // Returns false

obj.str = "";
(!!obj.str) // Returns false

obj.str = null;
(!!obj.str) // Returns false

It is concise and it works for undefined properties, although it's not the most readable.

Answer 34

You should always check for the type too, since JavaScript is a duck typed language, so you may not know when and how the data changed in the middle of the process. So, here's the better solution:

    let undefinedStr;
    if (!undefinedStr) {
      console.log("String is undefined");
    }
    
    let emptyStr = "";
    if (!emptyStr) {
      console.log("String is empty");
    }
    
    let nullStr = null;
    if (!nullStr) {
      console.log("String is null");
    }

Answer 35

There's no isEmpty() method, you have to check for the type and the length:

if (typeof test === 'string' && test.length === 0){
  ...

The type check is needed in order to avoid runtime errors when test is undefined or null.

Answer 36

If one needs to detect not only empty but also blank strings, I'll add to Goral's answer:

function isEmpty(s){
    return !s.length;    
}

function isBlank(s){
    return isEmpty(s.trim());    
}

Answer 37

1. check that var a; exist

2. trim out the false spaces in the value, then test for emptiness

    if ((a)&&(a.trim()!=''))
    {
      // if variable a is not empty do this 
    }
   

Answer 38

Meanwhile we can have one function that checks for all 'empties' like null, undefined, '', ' ', {}, []. So I just wrote this.

var isEmpty = function(data) {
    if(typeof(data) === 'object'){
        if(JSON.stringify(data) === '{}' || JSON.stringify(data) === '[]'){
            return true;
        }else if(!data){
            return true;
        }
        return false;
    }else if(typeof(data) === 'string'){
        if(!data.trim()){
            return true;
        }
        return false;
    }else if(typeof(data) === 'undefined'){
        return true;
    }else{
        return false;
    }
}

Use cases and results.

console.log(isEmpty()); // true
console.log(isEmpty(null)); // true
console.log(isEmpty('')); // true
console.log(isEmpty('  ')); // true
console.log(isEmpty(undefined)); // true
console.log(isEmpty({})); // true
console.log(isEmpty([])); // true
console.log(isEmpty(0)); // false
console.log(isEmpty('Hey')); // false

Answer 39

I use such approach

[null, undefined, ''].includes(value)

Answer 40

An alternative way, but I believe bdukes's answer is best.

var myString = 'hello'; 
if(myString.charAt(0)){
    alert('no empty');
}
alert('empty');

Answer 41

Here are some custom functions I use for handling this. Along with examples of how the code runs.

const v1 = 0
const v2 = '4'
const v2e = undefined
const v2e2 = null
const v3 = [1, 2, 3, 4]
const v3e = []
const v4 = true
const v4e = false
const v5 = {
  test: 'value'
}
const v5e = {}
const v6 = 'NotEmpty'
const v6e = ''

function isNumeric(n) {
  return !isNaN(parseFloat(n)) && isFinite(n)
}

function isEmpty(v, zeroIsEmpty = false) {
  /**
   * When doing a typeof check, null will always return "object" so we filter that out first
   * @see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/typeof#typeof_null
   */
  if (v === null) {
    return true
  }

  if (v === true) {
    return false
  }

  if (typeof v === 'object') {
    return !Object.keys(v).length
  }

  if (isNumeric(v)) {
    return zeroIsEmpty ? parseFloat(v) === 0 : false
  }

  return !v || !v.length || v.length < 1
}

console.log(isEmpty(v1), isEmpty(v1, true))
console.log(isEmpty(v2), isEmpty(v2e), isEmpty(v2e))
console.log(isEmpty(v3), isEmpty(v3e))
console.log(isEmpty(v4), isEmpty(v4e))
console.log(isEmpty(v5), isEmpty(v5e))
console.log(isEmpty(v6), isEmpty(v6e))

Also for reference, here's the source for Lodash isEmpty:

Answer 42

You can use lodash: _.isEmpty(value).

It covers a lot of cases like {}, '', null, undefined, etc.

But it always returns true for Number type of JavaScript primitive data types like _.isEmpty(10) or _.isEmpty(Number.MAX_VALUE) both returns true.

Answer 43

To check if it is empty:

var str = "Hello World!";
if(str === ''){alert("THE string str is EMPTY");}

To check if it is of type string:

var str = "Hello World!";
if(typeof(str) === 'string'){alert("This is a String");}

Answer 44

There is a lot of useful information here, but in my opinion, one of the most important elements was not addressed.

null, undefined, and "" are all falsy.

When evaluating an empty string, it's often because you need to replace it with something else.

In this case, you can expect the following behavior.

var a = ""
var b = null
var c = undefined

console.log(a || "falsy string provided") // prints ->"falsy string provided"
console.log(b || "falsy string provided") // prints ->"falsy string provided"
console.log(c || "falsy string provided") // prints ->"falsy string provided"

With that in mind, a method or function that can return whether or not a string is "", null, or undefined (an invalid string) versus a valid string is as simple as this:

const validStr = (str) => str ? true : false

validStr(undefined) // returns false
validStr(null) // returns false
validStr("") // returns false
validStr("My String") // returns true

Please note, you probably also want to trim() the string since "" !== " ".

Answer 45

It's a good idea too to check that you are not trying to pass an undefined term.

function TestMe() {
  if((typeof str != 'undefined') && str) {
    alert(str);
  }
 };

TestMe();

var str = 'hello';

TestMe();

I usually run into the case where I want to do something when a string attribute for an object instance is not empty. Which is fine, except that attribute is not always present.

Answer 46

Using core (read vanilla) javascript we can leverage Object.is() for strict equality comparison. Following is a code snippet.

function validateString(arg) {
 if (Object.is(arg, "") || Object.is(arg, null) || Object.is(arg, undefined)) {
      return false;
 }
 return true;
}

Here is the JavaScript spec: https://262.ecma-international.org/12.0/#sec-object.is

Here is the Mozilla Doc: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is

Hope this helps.

Answer 47

I usually use something like:

if (str == "") {
     //Do Something
}
else {
     //Do Something Else
}

Answer 48

A lot of answers, and a lot of different possibilities!

Without a doubt for quick and simple implementation the winner is: if (!str.length) {...}

However, as many other examples are available. The best functional method to go about this, I would suggest:

function empty(str)
{
    if (typeof str == 'undefined' || !str || str.length === 0 || str === "" || !/[^\s]/.test(str) || /^\s*$/.test(str) || str.replace(/\s/g,"") === "")
        return true;
    else
        return false;
}

A bit excessive, I know.

Answer 49

if ((input?.trim()?.length || 0) > 0) {
   // input must not be any of:
   // undefined
   // null
   // ""
   // " " or just whitespace
}

Or in function form:

const isNotNilOrWhitespace = input => (input?.trim()?.length || 0) > 0;

const isNilOrWhitespace = input => (input?.trim()?.length || 0) === 0;

Explanation:

If input is undefined or null then the null coalescing ?. will result in input?.trim()?.length will be undefined or null. ORing (||) that with 0 will give 0. 0 is not > 0 therefore the result will be false, ie it IS a nil value.

If input is empty or whitespace then .trim() will remove leading and ending whitespace, which will keep an empty input the same, and convert any whitespace to an empty value. The length of an empty string is then 0, and as above, 0 is not > 0, therefore the result will be false, ie it IS empty or only whitespace.

If input is any other string, it's length will be > 0 after calling .trim(), and therefore the result will be true, ie it IS NOT a nil value, and it IS NOT empty or only whitespace.

Answer 50

I would not worry too much about the most efficient method. Use what is most clear to your intention. For me that's usually strVar == "".

As per the comment from Constantin, if strVar could some how end up containing an integer 0 value, then that would indeed be one of those intention-clarifying situations.

Answer 51

var s; // undefined
var s = ""; // ""
s.length // 0

There's nothing representing an empty string in JavaScript. Do a check against either length (if you know that the var will always be a string) or against ""

Answer 52

If you need to make sure that the string is not just a bunch of empty spaces (I'm assuming this is for form validation) you need to do a replace on the spaces.

if(str.replace(/\s/g,"") == ""){
}

Answer 53

The closest thing you can get to str.Empty (with the precondition that str is a String) is:

if (!str.length) { ...

Answer 54

Try this:

export const isEmpty = string => (!string || !string.length);

Answer 55

I use a combination, and the fastest checks are first.

function isBlank(pString) {
    if (!pString) {
        return true;
    }
    // Checks for a non-white space character
    // which I think [citation needed] is faster
    // than removing all the whitespace and checking
    // against an empty string
    return !/[^\s]+/.test(pString);
}