How to check for 'undefined' anywhere in object chain?

Question

I would like to check if any object is missing in complex object chain. I've come up with following solution, is there a better way accomplish the same?

var lg = console.log;
var t = { a:{a1: 33, a12:{ aa1d: 444, cc:3 } }, b:00};
var isDefined = function(topObj, propertyPath) {
    if (typeof topObj !== 'object') {
        throw new Error('First argument must be of type \'object\'!');
    }
    if (typeof propertyPath === 'string') {
        throw new Error('Second argument must be of type \'string\'!');
    }
    var props = propertyPath.split('.');
    for(var i=0; i< props.length; i++) {
        var prp = props[i];
        lg('checking property: ' + prp); 
        if (typeof topObj[prp] === 'undefined') {
            lg(prp + ' undefined!');
            return false;
        } else {
           topObj = topObj[prp];
        }        
    }
    return true;
}
isDefined(t, 'a.a12.cc');

possible duplicate of [javascript test for existence of nested object key](http://stackoverflow.com/questions/2631001/javascript-test-for-existence-of-nested-object-key) — Felix Kling, Jul 27 '12 at 14:32
@Felix The question is not a duplicate. The duplicate does not account for inherit properties from the prototype chain. — Rob W, Jul 27 '12 at 14:51
@RobW: This was not asked for and is easy to change. The overall approach does not change. — Felix Kling, Jul 27 '12 at 15:14

dharcourt · Answer 1 · 2014-05-20T19:26:14.003

7

You could define your function more simply like this:

var isDefined = function(value, path) {
  path.split('.').forEach(function(key) { value = value && value[key]; });
  return (typeof value != 'undefined' && value !== null);
};

Working example on jsfiddle.

edited May 20 '14 at 19:26

answered Mar 07 '13 at 23:28

dharcourt

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score 3 · Accepted Answer · answered Jul 27 '12 at 14:38

3

Your concept is OK, but the code has to be changed. When a property has the null value, it can't have any properties. Trying to access a property on null results in an error. To fix this, use:

for (var i=0; i<props.length; i++) {
    var prp = props[i],
        val = topObj[prp];
    lg('checking property: ' + prp); 
    if (typeof val === 'undefined') {
        lg(prp + ' undefined!');
        return false;
    } else if (val === null) {
        return i === props.length-1; // True if last, false otherwise
    } else {
        topObj = val;
    }
}

answered Jul 27 '12 at 14:38

Rob W

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@krul Another catch: Don't use `var lg = console.log;` This breaks in Chrome. Use `var lg = console.log.bind(console);` instead, which preserves the context of `console.log`. – Rob W Jul 27 '12 at 14:59
Rob W, thanks, I know that but didn't pay attention, thanks anyway. – krul Jul 27 '12 at 15:38

score 0 · Answer 3 · answered Jan 09 '20 at 12:53

Keep it simple as you learned once in the theory. Try/catch the exception thrown within a custom function.

let obj1 = {
    x: {
        y: 10
    }
};

export function def(chain){
    try{
        let lookup = eval(chain);
        return true;
    } catch (e){
        return false;
    }
}

//true
document.write(def('obj1.x.y'));
//false (at any moment in the given chain)
document.write(def('obj1.k.v'));

How to check for 'undefined' anywhere in object chain?

3 Answers3