Pointing an 'object variable' with 'string value' and dynamically update it?

Question

I am trying to achieve a dynamic variable out of string value. The dynamic variable is the nested object. I used eval method of Javascript for that purpose. It worked as I expected.

To be more precise, here is the example:

var transport = [];
transport.vehicles[0].car.brake[2] = ['diskbrake','drumbrake']; 
var myString = "transport.vehicles[0].car.brake[2]"; 
var valueOfArray = eval(myString); 
console.log(valueOfArray);

Here, the console log gives me the desired output. But, I need to achieve something like dynamic update of 'transport' variable when I add new item to the "valueOfArray" variable.

valueOfArray.push('air brakes');

When I push the new value, it should also update 'transport' object.

Any guidance or suggestions would be very appreciable.

Thank you.

First, JS does not have associative arrays. Arrays are objects and hence you can play with it but its better to use Objects instead of arrays in such cases. Second, eval is bad practice. Search eval is evil for more info — Rajesh Dixit
– Rajesh Dixit, Commented Mar 14, 2017 at 7:11
If transport.vehicles[0].car.brake[2] refers to an array, your valueOfArray variable refers to that same array instance (not a copy of it), so if you use valueOfArray.push() you've added an item to transport.vehicles[0].car.brake[2]. — nnnnnn
– nnnnnn, Commented Mar 14, 2017 at 7:12
Also you cannot do something like var a = []; a[2].object.property.value. You will have to define these intermediate values before using them — Rajesh Dixit
– Rajesh Dixit, Commented Mar 14, 2017 at 7:15
@NirajPaudel In my opinion，you may need organize your data with OO ways. if you just use a path to retrieve the data,you know the data structure and the path,why didn't you access directly like transport.vehicles[0].car.brake[2]? this is easy and simple and error diagnosed.actually,resolve so deep path & retrieve data should be the work of the template engine. — holi-java
– holi-java, Commented Mar 14, 2017 at 8:03

Himanshu Pandey · Accepted Answer · 2017-03-14 08:11:46Z

1

Use lodash get, set. NPM module link. If you want to know how it is doing what it is doing in pure javascript, take a look at source code. Source code for get, set.

Example:

let object1 = { 'a': [{ 'b': { 'c': 3 } }] };
 _.get(object1, 'a[0].b.c');
// => 3

_.get(object1, ['a', '0', 'b', 'c']);
// => 3

_.get(object1, 'a.b.c', 'default');
// => 'default'


let object2 = { 'a': [{ 'b': { 'c': 3 } }] };

_.set(object2, 'a[0].b.c', 4);
console.log(object2.a[0].b.c);
// => 4

_.set(object2, ['x', '0', 'y', 'z'], 5);
console.log(object.x[0].y.z);
// => 5

So if you want to dynamically get and set an array, you can do it like this.

let object = {};
let array = _.get(object, 'transport.vehicles[0].car.brake[2]', []);
array.push('air brakes');
_.set(object, 'transport.vehicles[0].car.brake[2]', array);

JS Fiddle

edited Mar 14, 2017 at 8:11

answered Mar 14, 2017 at 7:15

Himanshu Pandey

7365 silver badges14 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Rajesh Dixit Over a year ago

Answer based on a library not tagged in question can get you downvotes.

Himanshu Pandey Over a year ago

Just trying to help out. He can take a look at source code instead, if he wants. I do not care much about my points, so you may as well downvote if you want. And probably he may not even know about the library, and if he already does, he would not have asked the question in first place. So, it will be wrong to expect him to add library tag.

Rajesh Dixit Over a year ago

Mate my comment was just a caveat. Your answer might be right, but adding a library to handle this case is wrong as the initial approach is wrong. It would help more if you also tell what is the right way to structure data and how to access them using paths in string. We all have partial knowledge and decide approach based on this partial approach and one wrong decision can make you do a lot of patch work.

Collectives™ on Stack Overflow

Pointing an 'object variable' with 'string value' and dynamically update it?

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related