TypeError: Cannot read property '$XXX' of undefined in Vue, how to solve it?

Vue.js is a very popular front-end framework that is widely used in the field of web development. However, when developing applications using Vue, we sometimes encounter the error message "TypeError: Cannot read property '$XXX' of undefined". This article will explain what this error means and provide some solutions to fix it.

1. What is "TypeError: Cannot read property '$XXX' of undefined"?

This error message will appear if we access an undefined property in Vue.js. Such as '$route', '$router' and other Vue-specific properties or custom properties. The error may also occur because the nested property or method does not exist.

2. Solution

2.1 Determine whether the property or method exists

We need to confirm whether the property or method exists in the vue instance. You can check whether the property or method exists in the vue instance in the developer tools.

2.2 Use the v-if directive

Using the v-if directive is usually the best way to determine whether a property or method exists in a vue instance. Use v-if to check whether the current property or method exists. If it exists, it will be displayed, otherwise it will not be displayed. The following sample code demonstrates how to use the v-if directive:

<div v-if="$route">
    <!-- 这里要展示$route属性 -->
</div>

2.3 Using special variables provided by Vue

Vue.js provides us with some special variables, such as $set and $delete . Properties can be operated on using these variables as follows:

this.$set(this.obj, 'newProp', 123);

2.4 Check if a nested property or method exists

We need to ensure that the nested property or method exists. The best way is to use the instance method $nextTick.

this.$nextTick(() => {
    if(this.obj && this.obj.data) {
        // 展示this.obj.data属性
    }
});

3. Summary

In Vue.js development, we need to know how to handle the 'Cannot read property '$XXX' of undefined' error, which can be done by checking the property or Whether the method exists, using the v-if directive and using special variables provided by Vue to solve such problems. The best way is to check if the nested property or method exists. I hope this article can be helpful to Vue.js developers.

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