Access Javascript nested objects safely

ECMAScript2020, and in Node v14, has the optional chaining operator (I've seen it also called safe navigation operator), which would allow your example to be written as:

var a = b?.c?.d;

From the MDN docs:

The optional chaining operator (?.) permits reading the value of a property located deep within a chain of connected objects without having to expressly validate that each reference in the chain is valid. The ?. operator functions similarly to the . chaining operator, except that instead of causing an error if a reference is nullish (null or undefined), the expression short-circuits with a return value of undefined. When used with function calls, it returns undefined if the given function does not exist.

This is an old question and now with es6 features, this problem can be solved more easily.

const idx = (p, o) => p.reduce((xs, x) => (xs && xs[x]) ? xs[x] : null, o);

Thanks to @sharifsbeat for this solution.

You can create a general method that access an element based on an array of property names that is interpreted as a path through the properties:

function getValue(data, path) {
    var i, len = path.length;
    for (i = 0; typeof data === 'object' && i < len; ++i) {
        data = data[path[i]];
    }
    return data;
}

Then you could call it with:

var a = getValue(b, ["c", "d"]);

Standard approach:

var a = b && b.c && b.c.d && b.c.d.e;

is quite fast but not too elegant (especially with longer property names).

Using functions to traverse JavaScipt object properties is neither efficient nor elegant.

Try this instead:

try { var a = b.c.d.e; } catch(e){}

in case you are certain that a was not previously used or

try { var a = b.c.d.e; } catch(e){ a = undefined; }

in case you may have assigned it before.

This is probably even faster that the first option.