Sometimes it's sticky...

Look at this code... what do you think is going to happen to the breeds array?

let breeds = ["Labrador","Akita","Siamese"] // Let's make an array of only Dogs Breed... splice out Siamese. let doggy = breeds; doggy.splice(2) console.log(doggy) // -> ["Labrador", "Akita"] console.log(breeds) // -> ["Labrador", "Akita"] 

So... we just wanted to change the doggy array, and not the breeds one.

We told JavaScipt:

1. I want a new array;
2. Call It doggy;
3. Give doggy the same values of Breeds;

let doggy = breeds; 

But Javascript with the "=" has created a REFERENCE.

With our declaration doggy and breeds are pointing at the "same object" by reference... the same memory, and by changing one, you're changing both!

Let's make a list... how not to create a reference

If we want to pass just the values of an array into another, and at the same time create a "new object".
We can use this useful methods.

//1. Create a copy with slice. let doggy = breeds.slice(); //2. Create a concatenation with an empty array. let doggy = [].concat(breeds); //3. Spread an array into another one. let doggy = [...breeds]; //4. Use the Array.from() method, to create an array, with the same value of //another one let doggy = Array.from(breeds); 

All the methods, up here, are creating a totally NEW doggy array, without any reference to the breeds one.
You can now take off the Siamese without any collateral effect.

let breeds = ["Labrador","Akita","Siamese"] let doggy = breeds.slice(); doggy.splice(2) console.log(doggy) // -> ["Labrador", "Akita"] console.log(breeds) // -> ["Labrador", "Akita", "Siamese"]