Accessing or creating nested JavaScript objects with string key without eval

Question

I am looking for a nice solution to access a property by string value, but if the property does not exist it should create it. If the root structure already has defined some

Answer 1

You could split the path and reduce the path by walking the given object. If no Object exist, create a new property with the name, or an array. Later assign the value.

function setValue(object, path, value) {
    var way = path.replace(/\[/g, '.').replace(/\]/g, '').split('.'),
        last = way.pop();

    way.reduce(function (o, k, i, kk) {
        return o[k] = o[k] || (isFinite(i + 1 in kk ? kk[i + 1] : last) ? [] : {});
    }, object)[last] = value;
}

var test = {};
setValue(test, "foo.name", "Mr. Foo");
setValue(test, "foo.data[0].bar", 100);
setValue(test, "and.another[2].deep", 20);
console.log(test);

Answer 2

I wouldn't reinvent the wheel in this case, and instead use lodash. Specifically the set() function. As per their example:

var object = { 'a': [{ 'b': { 'c': 3 } }] };

_.set(object, 'a[0].b.c', 4);
console.log(object.a[0].b.c);
// => 4

_.set(object, ['x', '0', 'y', 'z'], 5);
console.log(object.x[0].y.z);
// => 5