使用变量值从 React 类的状态问题中检索对象值

Question

I have a state that appears like so:

this.state = {
  dag: {
       topField: '',
       leftField: '',
       centreField: '',
       rightField: '',
       bottomField: ''
   },

   currentNode: ''
}

The currentNode in my program gets updates with one of the five variable names which are in the dag object eg currentNode = 'rightField'.

In my program, I am trying to access the part of the dag which has the value stored in currentNode:

For instance, imagine currentNode = 'rightField' and that I am trying to log the rightField part of the dag object. Since I have found on other answers on StackOverflow, that to access the value of a variable it is common practice to write 'this[variable]' I have been trying this :

console.log(this.state.dag.this[currentNode]);

But I get errors for this which state that there is no 'rightField' of undefined. Yet I am still able to print the value using the explicit variable name ie console.log(this.state.dag.rightField); instead of console.log(this.state.dag.this[currentNode]);

Why is this and how do I actually use the variable holding the variable name (currentNode holding the position of right, left, top, etc) to get the correct part of the dag (right, left, top, etc)?

Answer 1

this.state.dag.this[currentNode] <- Wrong.

dag doesn't have 'this' as a property. You are considering this operator wrongly. You should learn more about it.

this.state.dag[currentNode] <- Right

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Property_accessors

As Robin mentioned in comment, make sure currentNode variable exists and it refers to this.state.currentNode