Javascript check string empty?

Mihai B. · Jan 15, 2017

Is there a universal JavaScript function that checks that a string is empty or has a value?
I can do this with PHP but with JavaScript, I am new to it.

kevinhng86 · Jan 15, 2017

Hi Mihai,

In Javascript there is a lot of way to check on a variable that is native to the program. However you have to utilise them in a way so they can produce something useful in your code. The below is the code example that will check all type of thing for you. The only thing missing is the isNaN() check. isNaN will check if it is Not a Number or not and will return true or false. Try the function below out. It will annoy you a bit from pop but I'm sure it will show you the basic of checking a variables. You can utilise some method from the below function into very complex task for example to validate user input. However this is the basic structure of it.

Code:

var a = {};
// && = and , || = or , ! = not , === = absolute equal to , == = equal to but does not need to be absolute (this one is very complicated to use, I can't explain its all here, just don't use this one if you do not really have to.)
// =  = declaring a variable, !== = not equal to.

function check(input){
	if ( input ===  null || input === undefined ){
    	alert("Variables wasn't defined");
    }
    
    if ( input.length === 0 ){
    	alert("This is a declared but empty variable");
    }

 	if ( !input ){
		alert("I'm empty, false, NaN, 0, undefined or empty");
    }
    
  	alert( typeof(input) ); // This will tell you what type I am.

	if ( typeof(input) === "object" && input instanceof Object && input instanceof Array ){
    	alert( "I'm an Array, which is also an Object in Javascript" );
        alert( "I can be an Object and not be an Array, however if am an Array I am also a class of object") ;
    	alert( "Notice how typeof tell you I'm an Object although I am an Array" );
    }
    
    if ( input instanceof Object && !(input instanceof Array) ){
    	alert( "I am for sure an Object but not an Array" );
    }

}

check(a)

energizedit · Jan 15, 2017

If you just want to check whether there's any value, you can do

Code:

if (strValue) {
    //do something
}

myvirtualst1008 · Jun 2, 2017

check for empty strings (""), null, undefined, false and the number 0 and Nan. Say, if a string is empty var name = "" then console.log(!name) returns true . this function will return true if val is empty, null, undefined, false, the number 0 or Nan.

Javascript check string empty?

Mihai B.

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Mihai B.

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