TypeError: Cannot read property '$XXX' of null in Vue, how to deal with it?

TypeError: Cannot read property '$XXX' of null in Vue, how to deal with it?

In Vue development, we often encounter similar errors: "TypeError: Cannot read property '$XXX' of null". This error usually occurs when trying to use a property or method, but the object of the property or method is null.

There are various reasons for this error. The following will introduce some common situations and corresponding processing methods.

1. The component has not been mounted yet
   When the component is being mounted, there may be situations where the properties or methods have not been correctly initialized. The solution to this problem is to place the code that uses the property or method in an appropriate lifecycle hook function.

For example, if you use a property in the component's created hook function, and this property is actually initialized in the mounted hook function, you will encounter this error. The solution is to put the code that uses this property in the mounted hook function.

2. Problems caused by asynchronous operations
   When it comes to asynchronous operations, there may be situations where properties or methods have not been initialized correctly. In this case, you can use the v-if directive to ensure that the corresponding content is only rendered after the property or method has been properly initialized.

For example, if you use a property in an asynchronous operation to obtain data, and the property is actually assigned a value after the asynchronous operation is completed, you will encounter this error. The solution is to use v-if to determine whether the attribute has been assigned a value, and only render the corresponding content when the attribute has been assigned a value.

3. Check whether the object is empty
   Another possible reason for this error is that the object you are using a property or method is empty. Before using a property or method, first check whether the object is empty. You can use JavaScript's traditional if statement or the optional chain operator (?.) to make a judgment.

For example, if you want to use a property of the this.$route object, but this.$route may be empty, you can first check whether this.$route is empty before using the property. The sample code is as follows:

if (this.$route) {
  console.log(this.$route.path);
}

Or use the optional chain operator:

console.log(this.$route?.path);

Through the above three methods, we can avoid "TypeError: Cannot read property '$XXX' of null" errors to ensure the normal operation of the code.

Summary:
When you encounter the "TypeError: Cannot read property '$XXX' of null" error in Vue development, you can consider the following processing methods: Place the code in the appropriate In the life cycle hook function, use v-if to determine whether the attribute has been assigned a value and check whether the object is empty. Choose one of them or use a combination of them according to the specific situation to ensure the reliability and correctness of the code.

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