How to directly modify v-model value using directives? - vue.js

Question

I've got form with dynamic number of input fields and i need to transliterate data, passed to this fields in 'live'. I wrote custom directive which do all job, but there is an a error -> it converts all chars except last one (should be привет->privet, while привет->priveт). This is my source code
directives: {
transliterate: {
update(element, binding) {
element.value = tr(element.value)
}
}
}
This is PUG (Jade)
input(v-model='requestHotels.travellers[index].first_name', v-transliterate='true')
tr - just function, which transliterate from ru to en
I knew why this happening, but i can't solve it by myself. Any ideas?

Answer 1

1) Consider using computed property instead of directive. Personally, I don't like directives because they can add alot of useless complexity to your code. But there are some complex cases where they can be really useful. But this one is not one of them.
export default {
data: () => ({
tranliteratedValue: ""
}),
computed: {
vModelValue: {
get() {
return this.tranliteratedValue;
},
set(value) {
this.tranliteratedValue = transl.transform(value);
}
}
}
};
Full example: https://codesandbox.io/s/039vvo13yv?module=%2Fsrc%2Fcomponents%2FComputedProperty.vue
2) You can use filter and transliterate during render
filters: {
transliterate(value) {
return transl.transform(value);
}
}
Then in your template:
<p>{{ value | transliterate }}</p>
Full example: https://codesandbox.io/s/039vvo13yv?module=%2Fsrc%2Fcomponents%2FFilter.vue
3) Transparent wrapper technique (using custom component)
The idea behind transparent wrapper is that you should create custom component that behave as build-in input (and accepts the same arguments) but you can intercept events and change behaviour as you'd like. In your example - tranliterate input text.
<textarea
v-bind="$attrs"
:value="value"
v-on="listeners"
/>
computed: {
listeners() {
return {
...this.$listeners,
input: event => {
const value = transl.transform(event.target.value + "");
this.$emit("input", value);
}
};
}
}
Full example: https://codesandbox.io/s/039vvo13yv?module=%2Fsrc%2Fcomponents%2Finc%2FTransliteratedInput.vue
Read more about Transparent wrapper technique here https://github.com/chrisvfritz/7-secret-patterns/blob/master/slides-2018-03-03-spotlight-export.pdf
You can check all 3 working approaches here https://codesandbox.io/s/039vvo13yv