How to use js to change the value of global variables in the uniapp project

With the popularity of the Internet, more and more companies are beginning to use mobile terminals to expand their business scope. What follows is higher and higher requirements for mobile terminal development. Among them, UniApp, as a cross-platform development framework, has received more and more attention. UniApp can be used to quickly develop applications for multiple platforms (including H5, mini programs, native APPs, etc.) and has many advantages. During the development process, we often need to change the value of global variables in js. So, how to achieve this in UniApp? This article will discuss this issue.

Definition of global variables in UniApp

The method of setting global variables in UniApp is the same as that in native JS. You can use var, let or const keyword defines variables. Different from native JS, UniApp's global variables need to be defined in the App.vue file. In the App.vue file, you can define a global variable globalData to save global variables.

<script>
export default {
    globalData: {
        userInfo: null
    },
    onLaunch: function() {
        // 应用程序启动时执行的操作
    }
}
</script>

In the above code, a global variable named userInfo is defined. In addition, in the onLaunch life cycle function, you can add some operations that need to be performed when the application starts.

Change the value of global variables in JS

In UniApp, you can directly use this.globalData to access global variables. At the same time, you can also use the getApp() method to obtain the application instance. This method returns an object with access to application global data. Application global data refers to all global variables and functions defined in App.vue.

const app = getApp();

// 改变全局变量
app.globalData.userInfo = {
    name: '小明',
    age: 18
};

In the above code, the application instance is obtained using the getApp() method and assigned to the variable app. Then, you can use app.globalData to access the global variable userInfo. In order to change the value of this variable, you can assign a new value (such as an object containing name, age, etc.) to the variable.

In addition to direct assignment, you can also use some operators and methods to change the value of global variables. For example:

app.globalData.userInfo.age += 1;

In the above line of code, the = operator is used to increase the age attribute of the global variable userInfo. This is also a way to change global variables.

Things to note

When using global variables, you need to pay attention to the following points:

1. Global variables should be in App.vue file and should not be redefined in other components. Otherwise, global variable values ​​may not be as expected.
2. The value of global variables should use a single data type whenever possible. For example, do not change a global variable from the number type to the object type, as this may cause other code to run abnormally.
3. Avoid frequently changing the value of global variables. Not only does this increase the complexity of your code, it can also lead to unnecessary errors.

Conclusion

In UniApp, the role of global variables is very important. It can be accessed and changed anywhere in the application. When defining global variables, you should follow the rules to avoid errors. When using global variables, you also need to pay attention to some details to avoid unnecessary problems. I believe that through the introduction of this article, readers will have a deeper and more comprehensive understanding of global variables in UniApp.

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