What should I do if "TypeError: Cannot read property 'xxx' of null" appears when using vuex in a Vue application?

In Vue applications, it is very common to use vuex for state management. However, sometimes some problems will occur when using vuex, such as "TypeError: Cannot read property 'xxx' of null" and other errors. This problem usually occurs when using a property in state, and the value of the property is null or undefined. This article will introduce how to solve this problem.

1. Determine whether the state attribute exists

When we use vuex, if a certain attribute is defined in the state, we need to judge it before using it. Make sure it exists. We can use the special method $store.getters provided in Vue, which can easily get the properties in the state and make judgments before getting them. When the obtained property is null or undefined, we can return a default value or perform corresponding processing.

Take the following example:

An attribute username is defined in the state:

state: {
    username: null
},

Use this attribute in the component:

<template>
    <div>
        <p>{{ $store.getters.username || '默认值' }}</p>
    </div>
</template>

When the attribute When it is null or undefined, the default value or "null" will be returned.

2. Assign a default value to state in mutation

In vuex, mutation is the only way to modify state. We can assign default values ​​to state in mutation to ensure that the properties in state are not null or undefined. When we call mutation, if the attribute in the state is null or undefined, we assign it to the default value or handle it accordingly through mutation.

Take the following example:

Define an attribute username in state:

state: {
    username: null
},

Assign a default value to username in mutation:

mutations: {
    setUsername(state, username) {
        state.username = username || '默认值';
    }
}

When we call mutation, if username is null or undefined, it will be assigned the default value or "null".

3. Use the default parameter attribute of ES6

In ES6, we can use the default parameter attribute to set default values ​​for method parameters. In vuex, we can use this feature to ensure that properties in state are not null or undefined.

Take the following example:

An attribute username is defined in the state:

state: {
    username: null
},

Use the default parameter feature of ES6 in mutation:

mutations: {
    setUsername(state, username = '默认值') {
        state.username = username;
    }
}

When we call mutation, if username is null or undefined, it will be assigned the default value or "null".

To sum up, when we use vuex in a Vue application and problems such as "TypeError: Cannot read property 'xxx' of null" occur, we can determine whether the state attribute exists and give it in the mutation Methods such as assigning default values ​​to state and using the default parameter feature of ES6 can solve the problem. Hope this article is helpful to everyone.

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