Thread: Issue with Salesforce Lightning Web Component (LWC) JavaScript Method Not Updating UI

Hi Everyone,

I'm working on a Lightning Web Component (LWC) in Salesforce, and I'm running into an issue where my JavaScript method updates the data, but the UI doesn't reflect the changes. Here's my scenario:

I have a simple form where users can update an object property. The data updates correctly in the background (confirmed via console logs), but the UI doesn't show the changes. Here's my code:

Code:

HTML (template.html):

<template>
    <lightning-card title="Update Object Property">
        <div>
            <lightning-input 
                label="Enter New Value" 
                value={newValue} 
                onchange={handleChange}>
            </lightning-input>
            <lightning-button 
                label="Update" 
                onclick={updateValue}>
            </lightning-button>
        </div>
        <div>
            <p>Current Value: {currentValue}</p>
        </div>
    </lightning-card>
</template>

JavaScript (myComponent.js):

import { LightningElement, track } from 'lwc';

export default class MyComponent extends LightningElement {
    @track currentValue = 'Old Value'; // The value shown in the UI
    newValue = ''; // Temporary storage for the input value

    handleChange(event) {
        this.newValue = event.target.value; // Updating the temporary value
        console.log('New Value Entered: ', this.newValue);
    }

    updateValue() {
        // Attempting to update the UI-bound value
        this.currentValue = this.newValue;
        console.log('Updated Current Value: ', this.currentValue);
    }
}

When I input a new value and click the "Update" button, the console log shows that currentValue is updated correctly. However, the <p> tag in the UI still displays the old value.

What am I missing here? How can I ensure the UI reflects the updated currentValue?

Thanks in advance!

---------- Post added 11-25-2024 at 10:28 PM ----------

Found a solution as follows but if you can find the better point it would be much appreciated:

The issue here stems from the fact that the @track decorator is no longer needed for primitive data types (like String, Number, or Boolean) in Lightning Web Components. However, if you face issues where the UI doesn't update as expected, there are a couple of areas to check:

1. Ensure Proper Binding
The @track decorator is useful for complex objects or arrays, but for primitives like String, simply updating the value should be enough. Make sure the property currentValue is being updated properly. The issue could lie in how you're assigning newValue to currentValue.


2. Use a Getter for Binding
If the UI is still not reactive, you can use a getter to derive the value dynamically, ensuring the UI always reflects the latest state.



Here's the corrected and improved code:

Updated javascript:

Code:

import { LightningElement } from 'lwc';

export default class MyComponent extends LightningElement {
    currentValue = 'Old Value'; // Primitive type, no need for @track
    newValue = ''; // Temporary storage for the input value

    handleChange(event) {
        this.newValue = event.target.value; // Update the temporary value
    }

    updateValue() {
        // Update the UI-bound value
        this.currentValue = this.newValue;
    }

    get displayValue() {
        // Using a getter ensures the UI always reflects the current state
        return this.currentValue;
    }
}

Updated html

Code:

<template>
    <lightning-card title="Update Object Property">
        <div>
            <lightning-input 
                label="Enter New Value" 
                value={newValue} 
                onchange={handleChange}>
            </lightning-input>
            <lightning-button 
                label="Update" 
                onclick={updateValue}>
            </lightning-button>
        </div>
        <div>
            <p>Current Value: {displayValue}</p>
        </div>
    </lightning-card>
</template>

Key Fixes:

1. Removed unnecessary @track decorator from currentValue since primitives don't need it.


2. Introduced a getter named displayValue for dynamically returning currentValue to ensure reactivity in the UI.


3. Kept newValue as a temporary variable for input binding.



The getter displayValue ensures that the UI always reflects the latest value of currentValue. If the property changes, the UI re-renders automatically.

This approach should resolve the issue, and your UI will now update as expected when the button is clicked.