Shulou(Shulou.com)06/03 Report--

Xiaobian to share with you why JavaScript to use the extension operator, I believe most people do not know how, so share this article for everyone's reference, I hope you have a lot of harvest after reading this article, let's go to understand it together!

The stretch operator was first introduced in ES6 and quickly became one of the most popular features. Despite the fact that the extension operator applies only to arrays, it has been suggested that its functionality could be extended to objects. This feature was eventually introduced in ES9.

Why use the extension operator

You might be thinking,"JavaScript already does the job, so why use the extension operator? "Let's start with invariance.

Oxford dictionary: immutability-unchanged or unable to change over time.

As a software development term, immutability refers to a value whose state cannot change over time. In fact, most values that are commonly used (primitive values such as strings, integers, etc.) are immutable.

However, one very special thing about JavaScript is that arrays and objects are actually mutable. This could become a big problem.

We have a variable Squirtle. Since he had just visited the Pokémon Center, the HP of this Jenny Turtle was 100.

Since you want another Jenny turtle, declare the variable anotherSquirtle, specifying the initial Squirtle as its value. After a hard battle, another jenny turtle was defeated. Therefore, access the HP of another Jenny turtle and change it to 0. Next, check the initial Squirtle by typing console.log and...

Wait. What? Initial Squirtle HP reduced to 0. How is this possible? What happened to poor Jenny turtle? There was a JavaScript mutation. The following will explain why.

When you create the anotherSquirtle variable and assign the initial Squirtle its value, you are actually assigning a reference to the memory location of the initial Squirtle object. This is because JavaScript arrays and objects are reference data types. Unlike primitive data types, reference data types point to memory addresses where actual objects/arrays are stored.

For ease of understanding, think of the reference data type as a pointer to a global variable. Changing the value of a reference data type is actually changing the value of a global variable.

This means that when you change the HP value of anotherSquirtle to 0, you are actually changing the HP value of the Squirtle object stored in memory to 0. This is why mySquirtle has an HP of 0-because mySquirtle is a reference to an object stored in memory and can be changed via the anotherSquirtle variable.

That's all for "Why use extension operators in JavaScript". Thanks for reading! I believe that everyone has a certain understanding, hope to share the content to help everyone, if you still want to learn more knowledge, welcome to pay attention to the industry information channel!

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.