CODEWITHSUNDEEP
javascriptvue.jsvuejs2vue-component
madeye
madeye

Reputation: 1406

Event from parent to child component

I have event that is generated in parent component and child has to react to it. I know that this is not recommended approach in vuejs2 and i have to do a $root emit which is pretty bad. So my code is this.

<template>
    <search></search>
    <table class="table table-condensed table-hover table-striped" v-infinite-scroll="loadMore" infinite-scroll-disabled="busy" infinite-scroll-distance="10">
        <tbody id="trans-table">
            <tr v-for="transaction in transactions" v-model="transactions">
                <td v-for="item in transaction" v-html="item"></td>
            </tr>
        </tbody>
    </table>
</template>

<script>
    import Search from './Search.vue';

    export default {
        components: {
            Search
        },
        data() {
            return { 
                transactions: [], 
                currentPosition: 0 
            }
        },
        methods: {
            loadMore() {
                this.$root.$emit('loadMore', {
                    currentPosition: this.currentPosition
                });
            }
        }
    }
</script>

As You can see loadMore is triggered on infinite scroll and event is being sent to child component search. Well not just search but since it's root it's being broadcast to everyone.

What is better approach for this. I know that i should use props but I'm not sure how can i do that in this situation.

Upvotes: 7

Views: 13044

Answers (2)

Alvaro Fla&#241;o Larrondo
Alvaro Fla&#241;o Larrondo

Reputation: 5734

I think that @tobiasBora's comment on @Roy J's answer is pretty important. If your component gets created and destroyed multiple times (like when using v-if) you will end with your handler being called multiple times. Also the handler will be called even if the component is destroyed (which can turn out to be really bad).

As @tobiasBora explains you have to use Vue's $off() function. This ended up being non trivial for me beacuse it needed a reference to the event handler function. What I ended up doing was define this handler as part of the component data. Notice that this must be an arrow function, otherwise you would need .bind(this) after your function definition.

export default {
    data() {
        return {
            eventHandler: (eventArgs) => {
                this.doSomething();
            }
        }
    },
    methods: {
        doSomething() {
            // Actually do something
        }
    },
    created() {
        this.bus.$on("eventName", this.eventHandler);
    },
    beforeDestroy() {
        this.bus.$off("eventName", this.eventHandler);
    },
}

Upvotes: 1

Roy J
Roy J

Reputation: 43899

Just have a variable (call it moreLoaded) that you increment each time loadMore is called. Pass that and currentPosition to your search component as props. In Search, you can watch moreLoaded and take action accordingly.

Update
Hacky? My solution? Well, I never! ;)

You could also use a localized event bus. Set it up something like this:

export default {
    components: {
        Search
    },
    data() {
        return {
            bus: new Vue(),
            transactions: [], 
            currentPosition: 0 
        }
    },
    methods: {
        loadMore() {
            this.bus.$emit('loadMore', {
                currentPosition: this.currentPosition
            });
        }
    }
}

and pass it to Search:

<search :bus="bus"></search>

which would take bus as a prop (of course), and have a section like

created() {
    this.bus.$on('loadMore', (args) => {
        // do something with args.currentPosition
    });
}

Upvotes: 29

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