Another TypeScript Novice Encounters the Error: TypeError - Trying to Assign Value to Undefined Property '3'

Question

Another TypeScript Novice Encounters the Error: TypeError - Trying to Assign Value to Undefined Property '3'

There seems to be an issue with the creation of the transitions Array, but I can't figure out why!

The text class

export enum STATE_ID { CGU, Initial, Previous, Question}
export enum CHOICE_ID {CGU_accepted, CGU_not_accepted}

export class STATE_MACHINE {
    constructor (context: string) {
    this.transitions_initialize()
}   
put_transition (source: STATE_ID, target: STATE_ID, label: CHOICE_ID): void 
{console.log(this.transitions.length.toString)
    this.transitions[source][label] = target
}
private transitions: STATE_ID[][] = new Array()
private transitions_initialize(): void {
    this.put_transition(STATE_ID.Initial, STATE_ID.Question,                                            
                                                     CHOICE_ID.CGU_accepted)
    this.put_transition(STATE_ID.Initial, STATE_ID.CGU,           
                                                 CHOICE_ID.CGU_not_accepted)
    }
}
new STATE_MACHINE("test")

The error

[Function: toString]
Z:\Documents\Phi\Developpement\TypeScript\test3\state_machine.js:45
    this.transitions[source][label] = target;
                                    ^
TypeError: Cannot set property '3' of undefined
    at STATE_MACHINE.put_transition (Z:\Docum................

Any thoughts on what might be causing this?

arrays typescript

Answer 1

Answer №1

If you're looking to work with a multidimensional array in TypeScript or JavaScript, one key step is initializing each element properly beforehand. Here's an example:

private grid: CELL_VALUE[][] = new Array()

In this snippet, we've essentially created an empty array called grid. It doesn't contain any elements yet. Each element within it should be of type CELL_VALUE[]. To ensure that these elements exist when needed, you must instantiate them first. For instance:

set_cell_value(row: number, column: number, value: CELL_VALUE): void {
  if (!this.grid[row]) {
    this.grid[row] = new Array()
  }
  this.grid[row][column] = value
}

This method is intended to address any issues caused by uninitialized elements.

I hope this explanation proves useful to you. Best of luck with your coding!

Answer 2

If you're looking to work with a multidimensional array in TypeScript or JavaScript, one key step is initializing each element properly beforehand. Here's an example:

private grid: CELL_VALUE[][] = new Array()

In this snippet, we've essentially created an empty array called grid. It doesn't contain any elements yet. Each element within it should be of type CELL_VALUE[]. To ensure that these elements exist when needed, you must instantiate them first. For instance:

set_cell_value(row: number, column: number, value: CELL_VALUE): void {
  if (!this.grid[row]) {
    this.grid[row] = new Array()
  }
  this.grid[row][column] = value
}

This method is intended to address any issues caused by uninitialized elements.

I hope this explanation proves useful to you. Best of luck with your coding!

Another TypeScript Novice Encounters the Error: TypeError - Trying to Assign Value to Undefined Property '3'

Answer №1

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