Error trying to use isset in JavaScript

In JavaScript there is no isset() . In PHP isset() has two functionalities: / p>

• Whether a variable is declared
• check that your value is not null

To check if the variable is declared in JavaScript you must use typeof .

typeof is a method that says what is the type of the variable, apparently not exactly what you want. But if you use typeof foo != 'undefined'; then you already have what you want, and typeof has the advantage of not generating errors if the variable is not declared.

So instead of

if((isset(n1)) && (isset(n2))){

    document.getElementById('resultado').innerHTML = n1 + n2;   
}

You can use:

if(typeof n1 != 'undefined'  && typeof n2 != 'undefined'){

    document.getElementById('resultado').innerHTML = n1 + n2;   
}

If you also want to check the second condition that isset() checks, ous whether the value of the variable is different from null , you can do a simple check if(n1 != null){ // fazer algo .

if ((n1 != undefined) && (n2 != undefined)){
    // Resto do código após verificar se ambas as variáveis estão ou não vazias
}

Or I'd prefer to change undefined to null in some situations, everything will depend on the value that is received in the variable through the Javascript debug in the browser.

EDIT

If values pass as a text, or rather as String in the function, you can compare it with double or single quotation marks. Example:

if ((n1 != '') && (n2 != '')){
    // Resto do código após verificar se ambas as variáveis estão ou não vazias
}