JavaScript does not understand what passing parameters is

JavaScript Don’t Understand What Passing Parameters is: Detailed Introduction

In the process of learning JavaScript, we often hear the concept of "passing parameters", but for beginners, this concept is not so easy to understand . This article will explain the parameter passing mechanism of JavaScript in detail to help beginners master this important concept.

What are parameters?

Simply put, parameters are entities used to pass information when a function is called. In JavaScript functions, we can define parameters for the function and pass parameters when calling the function. Inside the function, we can obtain the information passed in by accessing these parameters.

As shown in the simple example below, we define a parameter x when defining the function, and use this parameter for calculation inside the function:

function square(x) {
  return x * x;
}

console.log(square(5)); // 输出25

In the above example, we A value of 5 was passed as parameter when calling the function. Inside the function, we used this parameter for calculation and got a result of 25.

Types of function parameters

In JavaScript, there are no type restrictions for function parameters. That is, we can pass any type of value as a parameter, such as numbers, strings, objects, etc. Here is an example:

function describe(object) {
  console.log(`The name of the object is ${object.name}`);
  console.log(`The age of the object is ${object.age}`);
}

let person = {
  name: "Tom",
  age: 20
};

describe(person);

In this example, we define a describe function that receives an object as a parameter. Inside the function, we access the object and print out its properties. When calling the function, we pass an object containing name and age properties as parameters.

Parameter passing method

In JavaScript, parameters can be passed in two ways: value passing and reference passing. In pass-by-value, the function creates a copy of the argument and uses that copy inside the function. In pass-by-reference, the function uses the actual reference of the parameter, and changes to the parameter's value inside the function directly affect the original value.

Let’s take a look at the difference:

Value transfer

function changeValue(number) {
  number = number + 10;
  console.log(number);
}

let number = 10;
changeValue(number);
console.log(number);

In this example, we define a function changeValue, which receives a number as a parameter. Inside the function, we add 10 to the argument and print the result. In the main code snippet, we define a number variable and set its initial value to 10. Then we called the changeValue function, passing number as a parameter. Inside the function, we modify the value of the parameter and output the result. But in the main code segment, the value of number has not been modified, it is still 10.

This is because in value passing, the function creates a copy of the parameter and uses that copy inside the function. So modifying the parameter value inside the function will not affect the original value.

Passing by reference

function changeObject(object) {
  object.name = "Bob";
  console.log(object.name);
}

let person = {
  name: "Tom",
  age: 20
};

changeObject(person);
console.log(person.name);

In this example, we define a changeObject function that receives an object as a parameter. Inside the function, we modify the name attribute of the parameter and output the result. In the main code snippet, we define a person object and pass it as a parameter to the changeObject function. Inside the function, we modify the name attribute of the parameter and output the result. In the main code segment, we output the person's name attribute again and find that its value has been modified to "Bob".

This is because in reference transfer, the function will use the actual reference of the parameter, and changing the value of the parameter inside the function will directly affect the original value.

Summary

Function parameters are a very important concept in JavaScript. It is a very common operation to pass information through parameters when calling a function. When defining a function, we can define parameters of any type and calculate or modify them inside the function. When passing parameters, we can choose to pass by value or by reference, depending on actual needs. For beginners, understanding the parameter passing mechanism is one of the keys to learning JavaScript.

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