Vue js : _this.$emit is not a function

Question

I have created a Vue component call imageUpload and pass property as v-model

<image-upload v-model="form.image"></image-upload>

and within imgeUpload component I have this code

<input type="file" accept="images/*" class="file-input" @change="upload">

upload:(e)=>{

    const files = e.target.files;
    if(files && files.length > 0){
        console.log(files[0])
        this.$emit('input',files[0])
     }
}    

and I received

Uncaught TypeError: _this.$emit is not a function

Thanks

Answer 1

Do not define your method with a fat arrow. Use:

upload: function(e){
    const files = e.target.files;
    if(files && files.length > 0){
        console.log(files[0])
        this.$emit('input',files[0])

    }
} 

When you define your method with a fat arrow, you capture the lexical scope, which means this will be pointing to the containing scope (often window, or undefined), and not Vue.

Answer 2

This error surfaces if $emit is not on the current context/reference of this, perhaps when you're in the then or catch methods of a promise. In that case, capture a reference to this outside of the promise to then use so the call to $emit is successful.

<script type="text/javascript">
var Actions = Vue.component('action-history-component', {
        template: '#action-history-component',
        props: ['accrual'],
        methods: {
            deleteAction: function(accrualActionId) {
                var self = this;
                axios.post('/graphql',
                    {
                        query:
                            "mutation($accrualId: ID!, $accrualActionId: String!) { deleteAccrualAction(accrualId: $accrualId, accrualActionId: $accrualActionId) { accrualId accrualRate name startingDate lastModified hourlyRate isHeart isArchived minHours maxHours rows { rowId currentAccrual accrualDate hoursUsed actions { actionDate amount note dateCreated } } actions {accrualActionId accrualAction actionDate amount note dateCreated }} }",
                        variables: {
                            accrualId: this.accrual.accrualId,
                            accrualActionId: accrualActionId
                        }
                    }).then(function(res) {
                    if (res.data.errors) {
                        console.log(res);
                        alert('errors');
                    } else {
                        self.$emit('accrualUpdated', res.data.data.deleteAccrualAction);
                    }
                }).catch(function(err) {
                    console.log(err);
                });
            }
        }
    });