I saw this question, but I didn't see a JavaScript specific example. Is there a simple string.Empty
available in JavaScript, or is it just a case of checking for ""
?
null
or undefined
empty? An empty string is an empty string, it is not null
or undefined
If you just want to check whether there's a truthy value, you can do:
if (strValue) {
//do something
}
If you need to check specifically for an empty string over null, I would think checking against ""
is your best bet, using the ===
operator (so that you know that it is, in fact, a string you're comparing against).
if (strValue === "") {
//...
}
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.
if (variable == constant value)
and if you forget an '=' then you're assigning the constant value to the variable instead of testing. The code will still work as you can assign variable in a if. So a safer way to write this condition is to reverse the constant value and the variable. This way when you test your code you'll see an error (Invalid lef-hand side in assignment). You can also use something like JSHint to disallow assignment in conditions and be warned when you write one.
if blue is the sky
. See dodgycoder.net/2011/11/yoda-conditions-pokemon-exception.html
if (!str) { // i am sure str is empty null or undefined here if I'm sure it won't be another data type }
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 " ")
if(str)
and if(!!str)
?
var any = (!!str1 && !!str2 && !!str3)
handling if there is a number in there as well
!!str.trim()
to make sure the string is not made of whitespaces only.
Boolean(str)
is a lot more readable and less "wtfish".
if
, it converts falsy values to false
and truthy values to true
. A if
block either executes or not based on wether the expression is truthy, there is no point adding !!
The closest thing you can get to str.Empty
(with the precondition that str is a String) is:
if (!str.length) { ...
str.Empty
.
length
attribute. Arrays do as well.
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,"") == ""){
}
if(str.match(/\S/g)){}
str.match(/\S/)
/\S/.test(str)
is better than str.match(/\S/)
because it doesn't bother with returning an array of matched results (might be micro performance gain there). Also, when just testing a string against a regexp, use the RegExp .test()
method to better convey that intent.
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
typeof
in the switch
did not work for me. I added a if (typeof e == "undefined")
test and that works. Why?
case typeof(e) == "undefined":
is wrong; that matches an e
of false
, not of undefined
. Apparently this was a suggested edit which got approved. The original case typeof this == "undefined":
still doesn’t make any sense. There’s also no reason to consider false
, 0
, and "0"
“empty”.
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
https://i.stack.imgur.com/bFeGV.png
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")} ${f(" ")}`); log1('A', A); log1('B', B); log1('C', C); log1('D', D); log1('E', E); log1('F', F); log1('G', G); log1('H', H); log2('I', I); log2('J', J); log3('K', K); log3('L', L); log3('M', M); log3('N', N); log3('O', O); log3('P', P); log3('Q', Q); log3('R', R);
And then for all methods I perform speed test case str = ""
for browsers Chrome v78.0.0, Safari v13.0.4, and Firefox v71.0.0 - you can run tests on your machine here
https://i.stack.imgur.com/IxaPG.png
You can use lodash: _.isEmpty(value).
It covers a lot of cases like {}
, ''
, null
, undefined
, etc.
But it always returns true
for Number
type of JavaScript primitive data types like _.isEmpty(10)
or _.isEmpty(Number.MAX_VALUE)
both returns true
.
_.isEmpty(" "); // => false
" "
is not empty. _.isEmpty("");
returns true.
Very generic "All-In-One" Function (not recommended though):
function is_empty(x)
{
return ( //don't put newline after return
(typeof x == 'undefined')
||
(x == null)
||
(x == false) //same as: !x
||
(x.length == 0)
||
(x == 0) // note this line, you might not need this.
||
(x == "")
||
(x.replace(/\s/g,"") == "")
||
(!/[^\s]/.test(x))
||
(/^\s*$/.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.
if
statement.
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 ""
There's nothing representing an empty string in JavaScript.
. What about ""
, doesn't that represent an empty string?
Try:
if (str && str.trim().length) {
//...
}
str.trim().length
will do faster than str.trim()
, by around 1% according to my own testing result.
if (!str) { ... }
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.
===
would be better. It only returns true if strVar
is an empty string.
You could also go with regular expressions:
if((/^\s*$/).test(str)) { }
Checks for strings that are either empty or filled with whitespace.
A lot of answers, and a lot of different possibilities!
Without a doubt for quick and simple implementation the winner is: if (!str.length) {...}
However, as many other examples are available. The best functional method to go about this, I would suggest:
function empty(str) { if (typeof str == 'undefined' || !str || str.length === 0 || str === "" || !/[^\s]/.test(str) || /^\s*$/.test(str) || str.replace(/\s/g,"") === "") return true; else return false; }
A bit excessive, I know.
str.length === 0
returns true for any function that has no formal parameters.
check that var a; exist trim out the false spaces in the value, then test for emptiness if ((a)&&(a.trim()!='')) { // if variable a is not empty do this }
" "
is not empty, but it would be considered empty by this condition.
I usually use something like this,
if (!str.length) {
// Do something
}
typeof variable != "undefined"
before checking if is empty.
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.
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());
}
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
value = false
or value = 0
. will you return the correct response according to the question?
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);
}
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.).
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
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; } }]
];
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
Trimming whitespace with the null-coalescing operator:
if (!str?.trim()) {
// do something...
}
?.
couldn't be less complicated. .trim()
would throw an error if str
is nullish.
Try this:
export const isEmpty = string => (!string || !string.length);
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.
empty(0)
and empty(7)
should return the same value.
empty("0")
must return false
(because that is a not empty string), but empty(0)
must return true
because it is empty :)
empty
is a misleading name in this case.
empty
is good. In php docs for empty function: Returns FALSE if var exists and has a non-empty, non-zero value. Otherwise returns TRUE.
The difference between PHP
and this function - that string '0'
will be not identified as empty.
empty
is an inaccurate and misleading name. It's interesting that PHP also has a poorly-named empty
function, but PHP's failings don't have anything to do with JavaScript.
if ((str?.trim()?.length || 0) > 0) {
// str must not be any of:
// undefined
// null
// ""
// " " or just whitespace
}
Update: Since this answer is getting popular I thought I'd write a function form too:
const isNotNilOrWhitespace = input => (input?.trim()?.length || 0) > 0;
const isNilOrWhitespace = input => (input?.trim()?.length || 0) === 0;
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
.
test === ""
is equivalent, and it's shorter.
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.
undefined
or null
Success story sharing
=== ''
vs.length
didn't show any discernible improvement (and using.length
only works if you can assume that you have a string).length > 0
is actually much faster than comparing to a string literal! Check out this jsPerf