I don't understand why I keep receiving the error message "Cannot read property 0 of undefined" even though the object clearly exists and I am attempting to access it within the correct scope

Question

I don't understand why I keep receiving the error message "Cannot read property 0 of undefined" even though the object clearly exists and I am attempting to access it within the correct scope

Here is a function example:

(function iterate(index) {

  var obj = { 0:{name:"John Doe"}, 1:{age: 30}, 2:{years: 5} };

  setTimeout(function() {
    //code ...
  }, (obj[0][years]*1000) );

)(0);

Encountering an error in the second last line

myscript.js:7 Uncaught TypeError: Cannot read property '0' of undefined

This issue points to a scoping problem, as attempts to access the 0th key using obj[0] or obj.0 have been unsuccessful.

Based on my understanding, the obj variable is defined in the same scope as the setTimeout() function call. So, what is causing this error and how can it be resolved?

javascript arrays json scope javascript-objects

Answer 1

Answer №1

When attempting to access the value of [seconds] using bracket notation, it first evaluates the variable seconds to determine the property to access. To avoid any potential errors, specify it in string format like ['seconds'] or use period notation as shown here:

var someObject = { 0:{some:"one"}, 1:{thing:"none"}, 2:{seconds: 5} };

try {
  console.log(someObject[2][seconds]*1000);
} catch (e) {
  console.log(e.message);
}
console.log(someObject[2].seconds*1000);

Furthermore, it is important to note that someObject[0] is {some: "one"}, which does not contain a seconds parameter. It seems like you intended to reference someObject[2] instead.

Answer 2

When attempting to access the value of [seconds] using bracket notation, it first evaluates the variable seconds to determine the property to access. To avoid any potential errors, specify it in string format like ['seconds'] or use period notation as shown here:

var someObject = { 0:{some:"one"}, 1:{thing:"none"}, 2:{seconds: 5} };

try {
  console.log(someObject[2][seconds]*1000);
} catch (e) {
  console.log(e.message);
}
console.log(someObject[2].seconds*1000);

Furthermore, it is important to note that someObject[0] is {some: "one"}, which does not contain a seconds parameter. It seems like you intended to reference someObject[2] instead.

I don't understand why I keep receiving the error message "Cannot read property 0 of undefined" even though the object clearly exists and I am attempting to access it within the correct scope

Answer №1

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