Question about Challenge answer and using const ?

Question

This is the challenge answer:
```JavaScript
const warning = document.getElementById("warning");
let button;
button = document.getElementById('makeItRed');
button.addEventListener( 'click', () => {
  warning.style.backgroundColor = 'red';
});
```
I want to know:
```JavaScript
const warning = document.getElementById("warning"); // we used const
let button;
button = document.getElementById('makeItRed');
button.addEventListener( 'click', () => {
  warning.style.backgroundColor = 'red';  // Why is there no error here?
});
```
"const" does not allow a variable to be redefined, yet this give no error, Why ? For example, the code below will give an error. I would think the above code would only work if we wrote let warning = document.getElementById("warning"); instead of using const warning. I still do not see how this event handler can give no error if it seems to be breaking the rule for "const", since it assigns const a new value  ?
This gives Error , since it would only work if we use "Let" :
JavaScript
const dog = 'barking';
dog = dog.style.color = 'red';
console.log(dog);

andren · Accepted Answer

With a const variable you cannot change what object it is assigned to, but the object itself can change. Take an array for example:
JavaScript
const names = ["James"];
names.push("Mary");
console.log(names);

In the above code I assign a list to the constant names and then add a name to that list, that is completely valid code because I have not assigned a different list to the constant, only changed what is present in said list.
If I were to do this however:
JavaScript
const names = ["James"];
names = ["James", "Mary"]
console.log(names);

Then that would not work, because in that case I actually am assigning a new list to the constant, rather than just changing the one that is already assigned to it.
The code in your example is the same, you don't assign a different HTML object to the constant, you just change a property of the object. In your second example you are trying to actually change what object is stored in the constant which is invalid, strings also don't have a style property so that example wouldn't work regardless but that is somewhat beyond the point.

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ian izaguirre

ian izaguirre

Question about Challenge answer and using const ?

1 Answer

andren

andren

ian izaguirre

ian izaguirre