Update values in a json object based on dynamic keys available as array

Though you are using Underscore, Lodash is 100% compatible with Backbone and can replace Underscore and it offers _.get and _.set for your specific case.

The path can be in an array or it can be a string. It even handles accessing array indexes.

_.get(object, path, [defaultValue])

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

_.get(object, 'a[0].b.c');
// => 3

_.get(object, ['a', '0', 'b', 'c']);
// => 3

_.get(object, 'a.b.c', 'default');
// => 'default'

_.set creates missing objects and arrays along the path if they do not exist.

_.set(object, path, value)

_.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

There's even a _.result function which calls the value if it's a function.

_.result(object, path, [defaultValue])

var object = { 'a': [{ 'b': { 'c1': 3, 'c2': _.constant(4) } }] };

_.result(object, 'a[0].b.c1');
// => 3

_.result(object, 'a[0].b.c2');
// => 4

_.result(object, 'a[0].b.c3', 'default');
// => 'default'

_.result(object, 'a[0].b.c3', _.constant('default'));
// => 'default'

Based on Nina's answer, to set the value, you could do something like the following, having a path which stops at before the last key, and use the last key to update the object manually.

function getValue(object, path) {
    return path.reduce(function (o, k) {
        return (o || {})[k];
    }, object);
}

var obj = { "glossary": { "title": "example glossary", "GlossDiv": { "title": "S", "GlossList": { "GlossEntry": { "ID": "SGML", "SortAs": "SGML", "GlossTerm": "Standard Generalized Markup Language", "Acronym": "SGML", "Abbrev": "ISO 8879:1986", "GlossDef": { "para": "A meta-markup language, used to create markup languages such as DocBook.", "GlossSeeAlso": ["GML", "XML"] }, "GlossSee": "markup" } } } } };


var target = getValue(obj, ['glossary', 'GlossDiv']);

target.title = "test";

console.log(obj);

Or as a new function, which takes a value directly and does all the job.

function setValue(object, path, value) {
  var target = path.slice(0, -1).reduce(function(obj, key) {
    return (obj || {})[key];
  }, object);
  target[path[path.length-1]] = value;
}

var obj = { "glossary": { "title": "example glossary", "GlossDiv": { "title": "S", "GlossList": { "GlossEntry": { "ID": "SGML", "SortAs": "SGML", "GlossTerm": "Standard Generalized Markup Language", "Acronym": "SGML", "Abbrev": "ISO 8879:1986", "GlossDef": { "para": "A meta-markup language, used to create markup languages such as DocBook.", "GlossSeeAlso": ["GML", "XML"] }, "GlossSee": "markup" } } } } };



setValue(obj, ['glossary', 'GlossDiv', 'GlossList', 'GlossEntry', 'GlossSee'], "my test value");

console.log(obj);

Nina's answer would be my preferred way of doing this. For those not yet familiar with functional programming or reducing, a simple forEach will do the trick. Good for comparison.

var config = {
  name: "foo",
  email: "bar",
  photo: {
    small: "somelink",
    large: "largelink"
  }
};

var keys = ['photo', 'large'];
var prevRef = config, ref;

keys.forEach(function(val, index) {
  console.log(val);
  ref = prevRef[val];
  prevRef = ref;
});

console.log(ref);