[Javascript] Primitive value are immutable

Primitive Values

Undefined (undefined), used for unintentionally missing values. Null (null), used for intentionally missing values. Booleans (true and false), used for logical operations. Numbers (-100, 3.14, and others), used for math calculations. Strings ("hello", "abracadabra", and others), used for text. Symbols (uncommon), used to hide implementation details. BigInts (uncommon and new), used for math on big numbers.

There is a old bug in Javascript which is typeof(null) === 'object', null is primitive value actually, but we have to live with this bug, fix it will break the world.

Primitive are immutable!

let reaction = 'yikes';
reaction[0] = 'l';
console.log(reaction);

What's the output of console log?

The Answer is:

yikes

In 'strict mode'; it will throw an error for that.

A String is a primitive value, and that means a great deal! All primitive values are immutable. Which means it is unchangeable, read-only. You can't mess with primitive values. AT ALL!

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Variables are not values, Variable point to values

let pet = 'Narwhal';
pet = 'The Kraken';
console.log(pet);

What's the output again?

The Answer is:

// "The Kraken"

But what about Primitive value are immutable? 

Yes, but here, we assign to 'pet' variable. We can change 'pet' variable to "The Kraken".