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
}
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.
Videos
They closed my question on SO because it's not reproducible, but that's exactly why I posted, because code isn't behaving as it should.
Anyway, I 'm receiving a JSON result from a web service. It looks something like this:
{ "data": [{ "id": "123ABC", "name" : "Test 1" }, { "id": "", "name" : "Test 2" }] }I 'm looping through the data array and need to determine if an id exists or not:
for( const item of data ) {
if( item.id !== null && item.id.trim().length > 0 ) {
doSomething();
} else {
doSomethingElse();
}
}My problem is that doSomething() fires for the first item ("123ABC") but also fires for the second where the id is empty.
I've tried spitting out the values for the second item:
console.log("NULL ", item.id === null);
console.log("EMPTY ", item.id.trim().length === 0);and results are
NULL false EMPTY false
so I'm wondering if there's something strange about the id value.
Starting with:
return (!value || value == undefined || value == "" || value.length == 0);
Looking at the last condition, if value == "", it's length MUST be 0. Therefore drop it:
return (!value || value == undefined || value == "");
But wait! In JS, 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
Q.E.D.
There are just a few revisions I would make.
First, always use === instead of == in Javascript. You can read more about that on Stack Overflow.
Second, since undefined is mutable, I would reccomend using
typeof value === "undefined"
instead of
value === undefined
Third, I would remove the !value and value === "" conditions. They are redundant.
My Revision
I would use a slightly different approach than you:
String.isNullOrEmpty = function(value) {
return !(typeof value === "string" && value.length > 0);
}
This checks if the type of the value is "string" (and thus non-null and not undefined), and if it is not empty. If so, it is not null or empty.
Note that this returns true for non-string inputs, which might not be what you want if you wanted to throw an error for an unexpected input type.