How to avoid 'cannot read property of undefined' errors?

Question

In my code, I deal with an array that has some entries with many objects nested inside one another, where as some do not. It looks something like the following:

Answer 1

I answered this before and happened to be doing a similar check today. A simplification to check if a nested dotted property exists. You could modify this to return the value, or some default to accomplish your goal.

function containsProperty(instance, propertyName) {
    // make an array of properties to walk through because propertyName can be nested
    // ex "test.test2.test.test"
    let walkArr = propertyName.indexOf('.') > 0 ? propertyName.split('.') : [propertyName];

    // walk the tree - if any property does not exist then return false
    for (let treeDepth = 0, maxDepth = walkArr.length; treeDepth < maxDepth; treeDepth++) {

        // property does not exist
        if (!Object.prototype.hasOwnProperty.call(instance, walkArr[treeDepth])) {
            return false;
        }

        // does it exist - reassign the leaf
        instance = instance[walkArr[treeDepth]];

    }

    // default
    return true;

}

In your question you could do something like:

let test = [{'a':{'b':{'c':"foo"}}}, {'a': "bar"}];
containsProperty(test[0], 'a.b.c');