ReferenceError: Invalid left-hand side in assignment when really assigning a value

Why does this snippet in node (10.5)

.then(function() {
this = {...this, ...payload};
this.update();
resolve({ok:true, node});
});


gives the following error:

ReferenceError: Invalid left-hand side in assignment


the payload holds a few properties that need to be added to this or if the property exists the property needs to be updated.

this

I do not understand why there is this error :(

You cannot assign this. Some more details : stackoverflow.com/questions/9713323/…
– Seblor
Jun 29 at 8:47

this

1 Answer
1

Well the Error is staightforward and says Invalid left-hand side in assignment, it means that you are using a wrong element in the left hand side of your assignment.

Invalid left-hand side in assignment

And that's because you are writing this = {...this, ...payload};, where you were trying to write a value to this in tour function, which is wrong and not possible, because you can't change this and assign a value to it as it's not permitted in JavaScript.

this = {...this, ...payload};

this

this

If you check the MDN this Reference you can see that:

In most cases, the value of this is determined by how a function is called. It can't be set by assignment during execution, and it may be different each time the function is called.

this

I see makes sense. Thank you
– Samuel
Jun 29 at 8:56

@Samuel You are welcome, glad it helps.
– chŝdk
Jun 29 at 8:57

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