What are some strategies for utilizing v-model in VueJS without altering the value?

Question

What are some strategies for utilizing v-model in VueJS without altering the value?

I am struggling with using the v-model directive to manage data in an input field. My goal is to monitor changes to this data, but when I try to watch it, the old and new values always appear identical. This behavior is a result of the data being mutated, as explained in the documentation: https://v2.vuejs.org/v2/api/#vm-watch

It's important to note that when mutating an Object or Array instead of replacing it entirely, the old and new values will be the same because they are referencing the same Object/Array. Vue does not store a separate copy of the value before mutation.

My question is, how can I use v-model without causing the data to be mutated?

javascript vue.js immutability

Answer 1

Answer №1

In order to track changes with $watch more effectively, consider using a separate data value instead of relying solely on the model bound variable. By doing this, you will have access to the previous value.

Example:

<div id="app">
    <input v-model="inputModel" type="text" />
</div>

Javascript Code:

var vm = new Vue({
    "el" : "#app",
    "data" : {
            "inputModel" : "",
            "inputValue" : ""
    },
    "methods" : {
        "changeHandler" : function(currentVal, prevVal) {
            console.log("Updating \"" + this.inputValue + "\" to \"" + currentVal + "\"");
            this.inputValue = currentVal;
        }
    }
});

vm.$watch("inputModel", vm.changeHandler);

Answer 2

In order to track changes with $watch more effectively, consider using a separate data value instead of relying solely on the model bound variable. By doing this, you will have access to the previous value.

Example:

<div id="app">
    <input v-model="inputModel" type="text" />
</div>

Javascript Code:

var vm = new Vue({
    "el" : "#app",
    "data" : {
            "inputModel" : "",
            "inputValue" : ""
    },
    "methods" : {
        "changeHandler" : function(currentVal, prevVal) {
            console.log("Updating \"" + this.inputValue + "\" to \"" + currentVal + "\"");
            this.inputValue = currentVal;
        }
    }
});

vm.$watch("inputModel", vm.changeHandler);

What are some strategies for utilizing v-model in VueJS without altering the value?

Answer №1

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