How to check an undefined argument of the function? (in JavaScript)

Question

There is some examples:

a = ''; //string
b = 0; //number 0
b1 = 0xf; //number 15
c = (function(){}) //function function (){}
d = []; //object
e = {}; //object [object Object]
f = void(0); //undefined undefined

but when I try pass undefined variable trougth function like that:

typeof qwerty; //undefined
function at(a){return (typeof a)+' '+a;}
at(qwerty); // ????

..i`v got an error "Uncaught ReferenceError: qwerty is not defined". How can I (Is the shortest way exist to) create function isDefined(a,b) or another trick to reduce that expression?:

c=(typeof a!='undefined'&&a||b)

Clarification: If a is defined - c equals a, overwise - b, like "c=@a?:b" in php

Edit:

function ud(_a){return typeof window[_a]==='undefined'}

a=undefined; b=3;
alert((ud('a')?4:a)+(ud('b')?5:b));

Do yourself a favour and search google.com for 'undefined value in javascript' - with a bit of reading and trying (Tryit Editor!) you will find the correct answer yourself — Tom Regner, Jan 12 '12 at 14:06
see http://stackoverflow.com/questions/27509/detecting-an-undefined-object-property-in-javascript — return1.at, Jan 12 '12 at 14:34

score 5 · Answer 1 · answered Jan 12 '12 at 12:05

5

function isDefined(variable, dflt) {
    return typeof variable === "undefined" ? dflt : variable;
}

var c = isDefined(a, b);

answered Jan 12 '12 at 12:05

Alex K.

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Uncaught ReferenceError: a is not defined (Google Chrome 16...) – iegik Jan 12 '12 at 20:04
Thats a problem with how your calling the function, you'll need to provide some sample code + all these examples assume that the test variable has been declared, is that not the case? – Alex K. Jan 13 '12 at 08:58
http://jsfiddle.net/iegik/grK5X seems to be argument have to declare before pass trougth the function, but it can be undefined. – iegik Jan 13 '12 at 19:38
1

It fails because in that case `a` is undefined & *undeclared* - the act of passing it to a function fails as js cant resolve the symbol `a` to anything. Move the check to inline rather than a function; http://jsfiddle.net/grK5X/3/ also see http://stackoverflow.com/questions/8531059/how-to-check-if-a-variable-or-object-is-undefined/8531113 – Alex K. Jan 14 '12 at 13:10

score 1 · Answer 2 · answered Jan 12 '12 at 12:00

1

function def( a, b ) {
    var undef;

    return a === undef ? b : a;
}

And then:

var c = def( a, b );
// if a is defined - c equals a, otherwise b

answered Jan 12 '12 at 12:00

Esailija

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How to check an undefined argument of the function? (in JavaScript)

2 Answers2