Shallow compare does check for equality. When comparing scalar values (numbers, strings) it compares their values. When comparing objects, it does not compare their attributes - only their references are compared (e.g. "do they point to same object?").
Let's consider the following shape of user
object
user = {
name: "John",
surname: "Doe"
}
Example 1:
const user = this.state.user;
user.name = "Jane";
console.log(user === this.state.user); // true
Notice you changed users name. Even with this change, the objects are equal. The references are exactly the same.
Example 2:
const user = clone(this.state.user);
console.log(user === this.state.user); // false
Now, without any changes to object properties they are completely different. By cloning the original object, you create a new copy with a different reference.
Clone function might look like this (ES6 syntax)
const clone = obj => Object.assign({}, ...obj);
Shallow compare is an efficient way to detect changes. It expects you don't mutate data.
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