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Discover how to resolve the `lookupReference is not a function` error in ExtJS and effectively retrieve field values using references. A comprehensive guide for developers.
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How to Get Value from Reference in ExtJS

If you’re working with ExtJS and have encountered the error message lookupReference is not a function when trying to access a field value through a reference in your store, you're not alone. This can be a common issue for developers utilizing the ExtJS framework. In this guide, we'll explore this problem, understand why it happens, and provide a clear solution to retrieve field values effectively.

Understanding the Problem

In ExtJS, references are a powerful way to link components together, particularly in complex applications. When using components like forms and stores, you might want to access a specific component using its reference name. Here’s a quick breakdown of the problem scenario:

Form Structure: You have a form with two comboboxes. One of the comboboxes has a reference name (terminal2).

Store Listener: In the listener's load function of your store, you attempt to access the field using this.lookupReference('terminal2').

Error Encountered: Instead of successfully accessing the reference, you get the error that lookupReference is not a function.

The Issue Explained

The error occurs because the store is not a component, and thus it doesn't have the lookupReference method. This method can only be utilized within component instances that are part of the component hierarchy.

Why lookupReference Doesn't Work in Stores

Non-component Nature: A store functions as a data source and does not inherit from the component class. Therefore, it lacks component-specific methods like lookupReference.

Reference Scoping: References are only valid within the context of the component that creates them, typically forms, panels, or containers.

Solution: Accessing References Correctly

To resolve the issue and correctly access the reference value, you can utilize the Ext.ComponentQuery class. Here’s how you can do it step-by-step:

Step 1: Modify Your Store Listener

Instead of using lookupReference, use the following line to get the reference directly:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Understanding the Code

Ext.ComponentQuery.query(): This method allows you to query the component tree and find components that match a specific selector. In this case, it looks for a combobox with the reference terminal2.

Checking Existence: Since querying might return an empty result, it's essential to check if the terminal field exists before trying to access its value.

Getting the Value: If the field exists, you can easily retrieve its current value using getValue().

Conclusion

By utilizing Ext.ComponentQuery.query(), you can effectively get the value of a reference field in your ExtJS application without running into errors. This approach not only resolves the lookupReference is not a function error but also enhances your ability to manage component interactions within your application.

If you have further questions about ExtJS or need help with other issues, feel free to reach out and join the community of developers! Happy coding!