I have a function to return if a variable/object is set or not:
function isset() {
var a = arguments, l = a.length;
if (l === 0) { console.log("Error: isset() is empty"); }
for (var i=0; i<l; i++) {
try {
if (typeof a[i] === "object") {
var j=0;
for (var obj in a[i]) { j++; }
if (j>0) { return true; }
else { return false; }
}
else if (a[i] === undefined || a[i] === null) { return false; }
}
catch(e) {
if (e.name === "ReferenceError") { return false; }
}
}
return true;
}
For example, this works:
var foo;
isset(foo); // Returns false
foo = "bar";
isset(foo); // Returns true
foo = {};
isset(foo); // Returns false
isset(foo.bar); // Returns false
foo = { bar: "test" };
isset(foo); // Returns true
isset(foo.bar); // Returns true
Here is the problem... if foo is never set to begin with, this happens:
// foo has not been defined yet
isset(foo); // Returns "ReferenceError: foo is not defined"
I thought I could use try/catch/finally to return false if error.name === "ReferenceError" but it isn't working. Where am I going wrong?
Edit:
So the answer below is correct. As I expected, you cannot access an undefined variable or trap it with try/catch/finally (see below for an explanation).
However, here is a not so elegant solution. You have to pass the name of the variable in quotes, then use eval to do the checking. It's ugly, but it works:
// Usage: isset("foo"); // Returns true or false
function isset(a) {
if (a) {
if (eval("!!window."+a)) {
if (eval("typeof "+a+" === 'object'")) { return eval("Object.keys("+a+").length > 0") ? true : false; }
return (eval(a+" === undefined") || eval(a+" === null") || eval(a+" === ''")) ? false : true;
}
else { return false; }
}
else { console.log("Empty value: isset()"); }
}
And just to follow up some more, I cleaned up the original function at the very top. It still has the same problem where if the variable doesn't exist you get a ReferenceError, but this version is much cleaner:
// Usage: isset(foo); // Returns true or false if the variable exists.
function isset(a) {
if (a) {
if (typeof a === "object") { return Object.keys(a).length > 0 ? true : false; }
return (a === undefined || a === null || a === "") ? false : true;
}
else { console.log("Empty value: isset()"); }
}