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

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

During the development process using Vue, we often encounter some errors. Among them, TypeError: Cannot read property 'XXX' of null is a common error type. This error usually occurs when using a property of an object, but the object is null or undefined.

So, how should we deal with this error when we encounter it?

First of all, we need to clarify the cause of this error. TypeError: Cannot read property 'XXX' of null means that we are trying to access the property of a null object. This means that when we access the properties of the object, we do not effectively judge or handle whether the object is null or undefined.

In order to solve this problem, we can take the following methods:

1. Use v-if or v-show for conditional judgment

In Vue In the template, we can use the v-if or v-show instructions to perform conditional judgment. By adding a conditional where the property is accessed, we can ensure that the property is only accessed if the object is not null or undefined.

For example, in the template we can write like this:

<div v-if="obj !== null">
  {{ obj.XXX }}
</div>

In this way, when the object is null, the content in the template will not be rendered, thus avoiding errors in accessing the null object.

2. Use ternary expressions for conditional judgment

In addition to using v-if or v-show for conditional judgment, we can also use ternary expressions for conditional judgment judge. By using a ternary expression where the property is accessed, we can use a default value if the object is null or undefined.

For example, in the Vue component we can write like this:

data() {
  return {
    obj: null
  }
},
computed: {
  objXXX() {
    return this.obj !== null ? this.obj.XXX : 'default value';
  }
}

In the template, we can access the computed property like a normal data property:

<div>
  {{ objXXX }}
</div>

When the object When null, the computed property returns a default value, thus avoiding errors in accessing null objects.

3. Use the optional chaining operator (Optional Chaining)

For projects with Vue versions greater than 2.0, we can also use the optional chaining operator (Optional Chaining). Handle this error. The optional chain operator can automatically determine whether the object is null or undefined when accessing the object's properties, and return undefined if the object is null or undefined.

For example, in the Vue component we can write like this:

data() {
  return {
    obj: null
  }
},
computed: {
  objXXX() {
    return this.obj?.XXX;
  }
}

In the template, we can access the computed property like a normal data property:

<div>
  {{ objXXX }}
</div>

When the object When it is null, the computed property will return undefined, thus avoiding the error of accessing the null object.

To sum up, when we encounter the TypeError: Cannot read property 'XXX' of null error in Vue, we can use v-if or v-show for conditional judgment, and use ternary expressions for conditional Determine, or use optional chaining operators for attribute access. These methods can effectively handle the error and ensure the normal operation of our application.

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