is there something like isset of php in javascript/jQuery? [duplicate]

Answer 1

http://phpjs.org/functions/isset:454

phpjs project is a trusted source. Lots of js equivalent php functions available there. I have been using since a long time and found no issues so far.

Answer 2

If you want to check if a property exists: hasOwnProperty is the way to go

And since most objects are properties of some other object (eventually leading to the window object) this can work well for checking if values have been declared.

Answer 3

JavaScript isset() on PHP JS

function isset () {
    // discuss at: http://phpjs.org/functions/isset
    // +   original by: Kevin van     Zonneveld (http://kevin.vanzonneveld.net)
    // +   improved by: FremyCompany
    // +   improved by: Onno Marsman
    // +   improved by: Rafał Kukawski
    // *     example 1: isset( undefined, true);
    // *     returns 1: false
    // *     example 2: isset( 'Kevin van Zonneveld' );
    // *     returns 2: true
    var a = arguments,
        l = a.length,
        i = 0,
        undef;

    if (l === 0) {
        throw new Error('Empty isset');
    }

    while (i !== l) {
        if (a[i] === undef || a[i] === null) {
            return false;
        }
        i++;
    }
    return true;
}

Answer 4

Not naturally, no... However, a googling of the thing gave this: http://phpjs.org/functions/isset:454

Answer 5

Try this expression:

typeof(variable) != "undefined" && variable !== null

This will be true if the variable is defined and not null, which is the equivalent of how PHP's isset works.

You can use it like this:

if(typeof(variable) != "undefined" && variable !== null) {
    bla();
}

Answer 6

in addition to @emil-vikström's answer, checking for variable!=null would be true for variable!==null as well as for variable!==undefined (or typeof(variable)!="undefined").