Utilizing Vue.js watcher to replicate input fields causing a null pointer error

I'm currently facing an issue in Vue.js while trying to set up a watcher for duplicating an input based on certain conditions. I keep encountering null references when using the value property, and I would appreciate it if someone could explain why this is happening so I can gain a better understanding of the problem.

Here is my HTML:

<div id="company-form">
    <label>Name</label>
    <input v-model="legalName" type="text"/>
    <label>Name To Call</label>
    <input v-model="communicationsName" />                      
</div>

This is my Vue code:

new Vue({
    el: '#company-form',
    data: {
        legalName: null,
        communicationsName: null,
    },
    watch: {
        legalName: function() {
            if (!this.communicationsName.value || this.legalName.value == this.communicationsName.value) {
                this.communicationsName.value = this.legalName.value;                       
            }
         }
     },
});

Upon checking the console, I found these errors:

[Vue warn]: Error in callback for watcher "legalName": "TypeError: Cannot read property 'value' of null"

vue.js:18 TypeError: Cannot read property 'value' of null

Answer №1

The v-model directive is utilized for establishing two-way data bindings.

Instead of writing this.communicationsName.value, simply use this.communicationsName.

The data property communicationsName already contains the desired value; it is not an instance of

HTMLInputElement</code, hence does not possess a <code>value
property.

You can try the following:

watch: {
    legalName: function() {
        //Check if communicationsName's value is null or equal to legalName's value before copying input field text
        if (!this.communicationsName || this.legalName == this.communicationsName) {
            this.communicationsName = this.legalName;                       
        }
     }
 },

Note: The if condition

this.legalName == this.communicationsName
might be unnecessary as the data properties already hold the same value.

Answer №2

Opt for using Computed Properties instead of other methods.

new Vue({
    el: '#company-form',
    data: {
        companyName: null,
    },
    computed: {
        officialName() {
           return this.companyName
         }
     },
});

Feel free to customize this code based on your specific needs.

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