Error trying to use isset in Javascript

Question

I don’t know what’s wrong with this Javascript code:

if( (isset(n1)) && (isset(n2)) ){
    document.getElementById('resultado').innerHTML = n1 + n2;   
}

I think I’m mixing PHP with JS. How can I fix this?

Answer 1

In Javascript does not exist isset(). In PHP the isset() has two features:

• whether a variable is declared
• verify that its value is not null

To verify that the variable is declared in Javascript you must use the typeof.

The typeof is a method that tells which is the guy variable, apparently not exactly what you want. But if you use typeof foo != 'undefined'; then you’ll 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 the isset() check, ous is if the value of the variable is different from null, you can do a simple check if(n1 != null){ // fazer algo.

Answer 2

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

Or I’d rather trade the undefined for null in some situations, everything will depend on the value received in the variable through the Javascript debug in the browser.

EDIT

If the values pass as a text, or rather as String in the function can be compared with double or single quotes. Example:

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