Related
I am trying to find a non-deprecated method of comparing two strings in Typescript and/or Javascript that can handle any string that can be generated using the special characters available on a standard keyboard, because our application is fetching a randomly generated password from the backend then displaying that in our PASSWORD and CONFIRM PASSWORD fields, instead of fetching the encrypted password from the DB and including it in the response, which could possibly be decrypted with enough effort by someone attempting to crack our password hashing algorithm.
It is comparing the PASSWORD to the CONFIRM PASSWORD and checking if they are equal using the 'eval()' function (because the validation condition is loaded from the DB, and could be "FIELD_1 > FIELD_2", not necessarily always equality checking. It does replacements using .replaceAll() on the condition based on form fields' current form value, then evaluates the conditions using eval(). However, replaceAll requires a regex, and regexes can't have certain special characters unescaped or else an error will occur.)
So, to try to find a solution that works for ALL strings/combinations of characters, I added code at the bottom of my question which will generate random strings and compare them for equality 3000 times, and if there are no issues, it will not print any failure messages. I noticed I can escape MOST strings successfully using the following:
function escapeSpecialCharactersInTestString(str: string) {
str = str.replace(/\$/g, '$$$$');
str = str.replace(/[']/g, "\\'");
return str;
}
However, it is still failing for strings like
\3aeB296Z=DH\D"]Yu[0;MC.dep.UeE8g]&}sz)6N|M?.]q:%/ because of the \3 giving the error Octal escape sequences are not allowed in strict mode. I don't want to have to disable strict mode somehow and shouldn't be required to. However, if I use the deprecated "escape()" function instead, it always works.
function escapeSpecialCharactersInTestString(str: string) {
return escape(str)
}
Looking for a solution that can replace any sequence of characters / any string, and I don't want to worry about using deprecated code.
Code that tests 3000 equal, randomly generated strings for equality and stops if it can't compare them:
const normalCharacters =
"0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
const specialCharacters = "#:;#&-?/%+*[]\\_=^!()|{}\",.";
function escapeSpecialCharactersInTestString(str: string) {
// console.log(str)
// WORKS 100% but is deprecated:
// str = escape(str)
str = str.replace(/\$/g, '$$$$');
str = str.replace(/[']/g, "\\'");
return str;
}
function generateRandomString(length: number) {
let characterList = normalCharacters + specialCharacters;
let result = "";
while (length > 0) {
let index = Math.floor(Math.random() * characterList.length);
result += characterList[index];
length--;
}
return result;
}
function evaluateConditionWithTrueOrFalseResult(testString: string) {
let conditionResult = false
let evalResult;
try {
evalResult = eval(testString);
} catch (e) {
console.log(e)
}
if (evalResult == true) {
conditionResult = true
} else if (evalResult == false) {
conditionResult = false
} else {
conditionResult = false
}
return conditionResult
}
function replaceAll(str: any, find: any, replace: any) {
//console.log("str: ",str,", find: ",find,", replace: ",replace)
if(str == null) {
return str;
}
if(find !== undefined && find !== null && find !== '' && find !== true && find !== false && !isDate(find) && isNaN(find)) {
find = escapeSpecialCharactersInTestString(find)
}
if(replace !== undefined && replace !== null && replace !== '' && replace !== true && replace !== false && !isDate(replace) && isNaN(replace)) {
//console.log("escaping special chars: ",replace)
replace = escapeSpecialCharactersInTestString(replace)
//console.log("after: ",replace)
}
// replaces whole word only because of the \\b 's
return str.replace(new RegExp('\\b' + find + '\\b', "g"),replace);
}
function isDate(val: any) {
let isDate = false
if(val !== undefined && val !== null) {
if(typeof val === 'object') {
if(val._isAMomentObject === true) {
isDate = true
}
}
if(Object.prototype.toString.call(val) === '[object Date]') {
isDate = true
}
}
// console.log("is ",val," a date: ",isDate)
return isDate
}
let myOrigString = "'PASSWORD' === 'CONFIRM_PASSWORD'";
for (let i = 0; i < 3000; i++) {
let formValue = generateRandomString(50)
let escapedFormValue = escapeSpecialCharactersInTestString(formValue)
let myReplacedString = replaceAll(myOrigString, 'PASSWORD', escapedFormValue)
myReplacedString = replaceAll(myReplacedString, 'CONFIRM_PASSWORD', escapedFormValue)
if (i > 0 && i % 100 == 0) {
console.log("at iteration: "+i)
}
if (evaluateConditionWithTrueOrFalseResult(myReplacedString) === false) {
console.log(myReplacedString, " failed at iteration: " + i)
break;
}
}
Is there a string.Empty in JavaScript, or is it just a case of checking for ""?
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
}
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.
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 " ")
The closest thing you can get to str.Empty (with the precondition that str is a String) is:
if (!str.length) { ...
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,"") == ""){
}
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
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")} ${f(" ")}`);
log1('A', A);
log1('B', B);
log1('C', C);
log1('D', D);
log1('E', E);
log1('F', F);
log1('G', G);
log1('H', H);
log2('I', I);
log2('J', J);
log3('K', K);
log3('L', L);
log3('M', M);
log3('N', N);
log3('O', O);
log3('P', P);
log3('Q', Q);
log3('R', R);
And then for all methods I perform speed test case str = "" for browsers Chrome v78.0.0, Safari v13.0.4, and Firefox v71.0.0 - you can run tests on your machine here
You can use lodash:
_.isEmpty(value).
It covers a lot of cases like {}, '', null, undefined, etc.
But it always returns true for Number type of JavaScript primitive data types like _.isEmpty(10) or _.isEmpty(Number.MAX_VALUE) both returns true.
Very generic "All-In-One" Function (not recommended though):
function is_empty(x)
{
return ( //don't put newline after return
(typeof x == 'undefined')
||
(x == null)
||
(x == false) //same as: !x
||
(x.length == 0)
||
(x == 0) // note this line, you might not need this.
||
(x == "")
||
(x.replace(/\s/g,"") == "")
||
(!/[^\s]/.test(x))
||
(/^\s*$/.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.
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 ""
Try:
if (str && str.trim().length) {
//...
}
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.
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*$/.test(str) || str.replace(/\s/g,"") === "")
return true;
else
return false;
}
A bit excessive, I know.
check that var a; exist
trim out the false spaces in the value, then test for emptiness
if ((a)&&(a.trim()!=''))
{
// if variable a is not empty do this
}
You could also go with regular expressions:
if((/^\s*$/).test(str)) { }
Checks for strings that are either empty or filled with whitespace.
I usually use something like this,
if (!str.length) {
// Do something
}
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());
}
if ((str?.trim()?.length || 0) > 0) {
// str 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;
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
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...
}
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 for an empty string, it's often because you need to replace it with something else.
In which 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
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.
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.
I have several strings that contain entries separated by a comma, for example:
('ENTRY1', 'ENTRY2','ENTRY3')
As you can see, each entry is separated by a comma, either with or without a following blank.
How can I check with JavaScript if between each entry there is always a comma (with or without a blank).
The string can contain 0 to n entries.
Requirement: A script should return true or false based on the following example:
('ENTRY1', 'ENTRY2','ENTRY3') // return false
('ENTRY1' 'ENTRY2''ENTRY3') // return true
('ENTRY1','ENTRY2''ENTRY3') // return true
false = correct entry
true = false entry
From your example:
('ENTRY1', 'ENTRY2','ENTRY3') // return false
('ENTRY1' 'ENTRY2''ENTRY3') // return true
('ENTRY1','ENTRY2''ENTRY3') // return true
Since entry is enclosed within single quote (' '), you can do
function validate(entries) {
if (entries.replace(/ /g, '').indexOf("''") > -1) {
return true;
} else {
return false;
}
}
//Test case
var entries1 = "('ENTRY1', 'ENTRY2','ENTRY3')";
var entries2 = "('ENTRY1' 'ENTRY2''ENTRY3')";
var entries3 = "('ENTRY1','ENTRY2''ENTRY3')";
document.write(validate(entries1)+","+validate(entries2)+","+validate(entries3));
You could use split like this:
var splitArray = someString.split(',');
for explicitly stating its separated by a ,
If I understand this correctly,
you can use regex for this to make sure there's always a comma between two items if your string is exactly as you mention above
var str = "('ENTRY1', 'ENTRY2','ENTRY3')";
str = str.match(/'([^'])+'/g).join(',');
since you updated your code you can use this code to achieve following
('ENTRY1', 'ENTRY2','ENTRY3') // return false
('ENTRY1' 'ENTRY2''ENTRY3') // return true
('ENTRY1','ENTRY2''ENTRY3') // return true
false = correct entry true = false entry
function isNotOK(str){
var match = str.match(/'[^,i]+'/g);
var len = str.match(/'([^'])+'/g)
if(match && len && match.length === len.length){
return false;
}
return true;
}
var str1 = "('ENTRY1', 'ENTRY2','ENTRY3')";
var str2 = "('ENTRY1' 'ENTRY2''ENTRY3')";
document.write(isNotOK(str1) + ' , ' + isNotOK(str2));
I need a JavaScript function to tell me whether a string object is empty. By "empty", I mean that it's not all just whitespace characters. I've written this prototype:
String.prototype.isEmpty = function() {
return this.length === 0 || this === " " || this.test(/^\s*$/);
}
Is this alright?
Is there a more-performant version of this out there?
Use
String.prototype.isEmpty = function() {
if (!this.match(/\S/)) {
return ('enter some valid input.Empty space is not allowed');
} else {
return "correct input";
}
}
alert("test 1:"+(" ".isEmpty()));
alert("test 2:"+(" \t ".isEmpty()));
alert("test 3:"+(" \n ".isEmpty()));
alert("test 4:"+("hi".isEmpty()));
Note:
\s will match a whitespace character: space, tab or new line.
\S will match non whitespace character:anything but not a space, tab or new line.
If your string has a single character which is not a space, tab or new line, then it's not empty.
Therefore you just need to search for one character: \S
It looks like you need to use /^\s*$/.test(this) instead of this.test(/^\s*$/). There is no test() method for strings, unless you're using some JavaScript library that implements this method.
The /^\s*$/.test(this) would have been enough, but the first two expressions would short circuit if any one of them evaluates to true, without having to test the regular expression. That should be pretty efficient.
As #Matthew Crumley noted in a comment above, your this === " " expression will always evaluate to false. You could remove this expression, or use == if you would will be expecting a lot of strings with just a single space character:
String.prototype.isEmpty = function() {
return this.length === 0 || this == " " || /^\s*$/.test(this);
}
String.prototype.isEmpty = function() {
return this.length == 0 || /^\s*$/.test(this);
}
There is just a possibility out of 255 (not considering Unicode characters with code greater than 255) that a string with length 1 contains the space character. Considering strings with lenght greater than 1, the possibility get even lower.
Generally, using RegExp.prototype.test for checking for a pattern match without compilation of a return array of matches (String.prototype.match) likely has a better performance. I'd try -- but haven't tested yet -- something like:
function isEmpty() {
var string = arguments[0] ;
var EMPTY_STRING_PATTERN = /^\s*$/ , empty = false ;
if( EMPTY_STRING_PATTERN.exec(string) === true ) empty = true ;
return empty ;
}
On a side note, it is considered bad practice to fiddle with the prototype object of core javascript objects.
from example https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/String/Trim
var orig=" foo "
document.write(orig.trim()) // foo
document.write(orig.trim().length) // 3
tested on FF 3.6.8, Safari 5.0.1, Google Chrome 5.0.375.127, but produce js error on IE 8
I fiddled with some of the things:
I'm returning the inverse of this.length, for 0 that is true, for everything other number that is false.
I removed the check for " ". I actually haven't seen much, if any cases where a single space was entered, removing the check is IMO faster on average.
And flipped the regex <-> string like the others did.
String.prototype.isEmpty = function() {
return !this.length || /^\s*$/.test(this);
}
Same answer as Daniel Vassallo originally provided, in example form.
String.prototype.isEmpty = function() {
return /^\s*$/.test(this);
}
document.body.style="background-color:black; color:green;font-size:12pt;font-family: 'Courier New', monospace;font-weight: bold";
String.prototype.isEmpty = function() {
return /^\s*$/.test(this);
}
let test0 = ''.isEmpty();
let test1 = '\xa0'.isEmpty();
let test2 = ' '.isEmpty();
let test3 = '\t'.isEmpty();
let test4 = '\n'.isEmpty();
let test5 = '\n\n'.isEmpty();
let test6 = '\n\t\n'.isEmpty();
let test7 = '\r\n'.isEmpty();
let test8 = '\r\t\n'.isEmpty();
let test9 = '\r\n\t'.isEmpty();
var texts = new Array(
("String.prototype.isEmpty = function() {"),
(" return /^\s*$/.test(this);"),
("}"),
(""),
("let test0 = ''.isEmpty() // " + test1),
("let test1 = ' '.isEmpty() // " + test2) + " (non breaking space)",
("let test2 = ' '.isEmpty() // " + test2),
("let test3 = '\\t'.isEmpty() // " + test3),
("let test4 = '\\n'.isEmpty() // " + test4),
("let test5 = '\\n\\n'.isEmpty() // " + test5),
("let test6 = '\\n\\t\\n'.isEmpty() // " + test6),
("let test7 = '\\r\\n'.isEmpty() // " + test7),
("let test8 = '\\r\\t\\n'.isEmpty() // " + test8),
("let test9 = '\\r\\n\\t'.isEmpty() // " + test9)
);
texts.forEach(text => {
let nobreakchar = '\xa0'
;
document.body.append(document.createTextNode(text.replaceAll(" ",nobreakchar)))
document.body.append(document.createElement("br"))
});
Instead of writing more number of lines let's finish it in 2 lines only.
String.prototype.isEmpty = function () {
return this.length === 0 || this.trim() === ""
}
With trim() you don't need to worry about if the variable is only having space characters and that is how you can avoid those falling in regex
Is there a string.Empty in JavaScript, or is it just a case of checking for ""?
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
}
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.
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 " ")
The closest thing you can get to str.Empty (with the precondition that str is a String) is:
if (!str.length) { ...
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,"") == ""){
}
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
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")} ${f(" ")}`);
log1('A', A);
log1('B', B);
log1('C', C);
log1('D', D);
log1('E', E);
log1('F', F);
log1('G', G);
log1('H', H);
log2('I', I);
log2('J', J);
log3('K', K);
log3('L', L);
log3('M', M);
log3('N', N);
log3('O', O);
log3('P', P);
log3('Q', Q);
log3('R', R);
And then for all methods I perform speed test case str = "" for browsers Chrome v78.0.0, Safari v13.0.4, and Firefox v71.0.0 - you can run tests on your machine here
You can use lodash:
_.isEmpty(value).
It covers a lot of cases like {}, '', null, undefined, etc.
But it always returns true for Number type of JavaScript primitive data types like _.isEmpty(10) or _.isEmpty(Number.MAX_VALUE) both returns true.
Very generic "All-In-One" Function (not recommended though):
function is_empty(x)
{
return ( //don't put newline after return
(typeof x == 'undefined')
||
(x == null)
||
(x == false) //same as: !x
||
(x.length == 0)
||
(x == 0) // note this line, you might not need this.
||
(x == "")
||
(x.replace(/\s/g,"") == "")
||
(!/[^\s]/.test(x))
||
(/^\s*$/.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.
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 ""
Try:
if (str && str.trim().length) {
//...
}
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.
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*$/.test(str) || str.replace(/\s/g,"") === "")
return true;
else
return false;
}
A bit excessive, I know.
check that var a; exist
trim out the false spaces in the value, then test for emptiness
if ((a)&&(a.trim()!=''))
{
// if variable a is not empty do this
}
You could also go with regular expressions:
if((/^\s*$/).test(str)) { }
Checks for strings that are either empty or filled with whitespace.
I usually use something like this,
if (!str.length) {
// Do something
}
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());
}
if ((str?.trim()?.length || 0) > 0) {
// str 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;
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
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...
}
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 for an empty string, it's often because you need to replace it with something else.
In which 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
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.
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.