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Boolean conditionals with placeholder [duplicate]

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.

React Conditional Rendering, avoid 0 evaluated to false/undefined

I have checked the other Q/As. Mine is a bit different and I'm new to ReactJS.
Following code for setting const variable evaluates 0 as false/undefined
and value returned from myFunc is "" :
function formatAmount(x){
if(x === undefined || x === null) return "";
return(x.toLocaleString("en-US",{style: "currency", currency: "USD"}));
}
//When user.bill.amount == 0 this line evaluates it to false!!
const amount = user?.bill?.amount || user?.statement?.amount;
function myFunc(){
return(formatAmount(amount));
}
I tried expanding it with a function and IF conditions but the value returned by myFunc is "$NaN":
const amount = () => {
if(user?.bill?.amount || user?.bill?.amount === 0){
return user?.bill?.amount;
}
if(user?.statement?.amount || user?.statement?.amount === 0){
return user?.statement?.amount;
}
}
Expected:
When user.bill.amount == 0, myFunc should return "$0.00"
Actual:
myFunc returns empty string when user.bill.amount == 0

I think the problem here is 0 is falsy so when using || operator 0 will evaluate to false.
const amount = user?.bill?.amount || user?.statement?.amount;
If your environment supports the nullish operator that would work here.
const amount = user?.bill?.amount ?? user?.statement?.amount;

How can I test two strings for equivalence in JavaScript, considering null and empty string the same?

If I compare "a" and "b", that should be false.
If I compare "a" and "a", that should be true.
If I compare "" and null, that should be true.
I could write my own method, but thought there was perhaps a JavaScript shortcut.
Edit: I was thinking something like this:
areDbSame(s1, s2) {
if (s1 === null) s1 = "";
if (s2 === null) s2 = "";
return s1 === s2;
}
Edit2: Settled on this version:
areDbSame(s1, s2) {
return (s1 === null ? "" : s1) === (s2 === null ? "" : s2);
}

Just before you test the equality of your string, you could do a simple one line enforcement, by converting to '' in the case of null. For example (if you also don't care about undefined, false, etc):
// testString becomes the one you are testing
var testString = myString || '';
If you only want to ensure null is blank
var testString = (myString === null) ? '' : myString;
Then you can simply do your string comparisons using testString, and not worry about the null equalities.
IMO this is the cleanest answer because it doesn't convolute the original equality testing of javascript strings. It is the same as saying, let's split the problem up into two parts.
1) When should my string be considered blank, and
2) Now I can just check for regular string equality.

function areEqualStrings(a, b) {
var otherEqualValues = ['', null];
if(typeof a === 'string' && typeof b === 'string') {
return a === b;
} else if(otherEqualValues.indexOf(a) > -1 && otherEqualValues.indexOf(b) > -1) {
return !a === !b;
} else {
return false;
}
}
When coercing JavaScript values, !null is true and !'' is true, so those would result in being equal.
Here's the test (screenshotted from my console):

This function should do it. It type checks first and short circuits otherwise.
function stringCompare(a, b) {
if (((a === null || typeof a === 'string') ||
(b === null || typeof b === 'string')) &&
((a === '' && b === null) ||
(b === '' && a === null) ||
(a === b))) {
return true;
}
return false;
}

No it hasn`t. The two first cases you can do naturally using operator =.
The third case it is impossible because "" is considered a empty string and null has any type. So they never can be true naturally. To do this, you have to write your own method.
Just to be clear. You can use operators = (equal) to do comparison:
== equal to
`x == 8 false
x == 5 true
x == "5" true
=== equal value and equal type
x === 5 true
x === "5" false
Hope it helps

optional arguments and default value

I am new to javascript does the following 2 functions does the same thing and would you pick one over another?
var multiply = function(arg1, arg2) {
arg1 && (arg1 = 0);
arg2 && (arg2 = 0);
return arg1*arg2;
}
var multiply = function(arg1, arg2) {
arg1 = arg1 || 0;
arg2 = arg2 || 0;
return arg1*arg2;
}
the reason i am asking is i saw something like this for the first time
function(path, limit) {
var ref = firebaseRef(path);
limit && (ref = ref.limit(limit)); //if i understood correctly this line does an assignment based on condition without an if statement
return $firebase(ref);
}

function(path, limit) {
var ref = firebaseRef(path);
limit && (ref = ref.limit(limit)); // Important
return $firebase(ref);
}
The Important line, can be written like this
if (limit) {
ref = ref.limit(limit);
}
But if you wanted to write it like the first way, you would have done,
ref = limit && ref.limit(limit)
This has one problem, when limit is Falsy && immediately returns the evaluated Falsy value of limit, so ref is Falsy now. You wouldn't have wanted this, I believe.
At the end of the day, as a programmer, readability and maintainability of the code of the code what we write matters. So, I would recommend using an explicit if check, which I mentioned at the beginning of the answer.
Note: Also, as noted by others, the first multiply should have been like this
var multiply = function(arg1, arg2) {
arg1 || (arg1 = 0);
arg2 || (arg2 = 0);
return arg1 * arg2;
}
Even better, I would have written it like this
var multiply = function(arg1, arg2) {
return (arg1 || 0) * (arg2 || 0);
}

Both are variable assignments which evaluate differently on the logical operation.
For example expr1 && expr2 will return expr1 if expr1 returns false otherwise the variable assignment will evaluate to the second expression (i.e. expr2).
Using the logical-or operation will return expr1 if it evaluates to true, otherwise it will return expr2.
Consider the following:
// Logical AND
var a1 = true && true; // t && t returns true
var a2 = true && false; // t && f returns false
var a3 = false && true; // f && t returns false
var a4 = false && (3 == 4); // f && f returns false
var a5 = "Cat" && "Dog"; // t && t returns Dog
var a6 = false && "Cat"; // f && t returns false
var a7 = "Cat" && false; // t && f returns false
// Logical OR
var o1 = true || true; // t || t returns true
var o2 = false || true; // f || t returns true
var o3 = true || false; // t || f returns true
var o4 = false || (3 == 4); // f || f returns false
var o5 = "Cat" || "Dog"; // t || t returns Cat
var o6 = false || "Cat"; // f || t returns Cat
var o7 = "Cat" || false; // t || f returns Cat
For more information, see: Mozilla Developer Network on Logical Operator Expressions

I think the first one will actually do the opposite of what you want. Let's test this with a few cases:
arg1 && (arg1 = 0);
If arg1 is 0, or any other falsy value, so the execution goes as follows:
0 (meaning false) AND an assignment. The expression will immediately return false without executing the arg1 = 0 statement, because false || (t/f) always returns false.
If arg1 is 1, or any other truthy value, so we have:
1 (meaning true) AND an assignment. The assignment will run this time, because it has to see what the second condition returns. Therefore, arg1 will be set to 0.
The correct snippet is the second.

How do I check if a JavaScript parameter is a number?

I'm doing some trouble-shooting and want to add a check that a parameter to a function is a number. How do I do this?
Something like this...
function fn(id) {
return // true iff id is a number else false
}
Even better is if I can check that the parameter is a number AND a valid integer.

function fn(id) {
return typeof(id) === 'number';
}
To also check if it’s an integer:
function fn(id) {
return typeof(id) === 'number' &&
isFinite(id) &&
Math.round(id) === id;
}

i'd say
n === parseInt(n)
is enough. note three '===' - it checks both type and value

Check if the type is number, and whether it is an int using parseInt:
if (typeof id == "number" && id == parseInt(id))

=== means strictly equals to and == checks if values are equal.
that means "2"==2 is true but "2"===2 is false.
using regular expression
var intRegex = /^\d+$/;
if(intRegex.test(num1)) {
//num1 is a valid integer
}
example of
== vs. ===

function fn(id){
if((parseFloat(id) == parseInt(id)) && !isNaN(id)){
return true;
} else {
return false;
}
}

function fn(id) {
var x = /^(\+|-)?\d+$/;
if (x.test(id)) {
//integer
return true;
}
else {
//not an integer
return false;
}
}
Test fiddle: http://jsfiddle.net/xLYW7/