Cannot read property '_wrapper' of undefined in Vue.JS

Error: Cannot read property ‘_wrapper’ of undefined. I sometimes get these errors again, and then I forget how to fix them. So I rewrite here to remember it:

This error occurs when a v-on:click OR @click directive in the template is missing the function it’s pointing to, inside methods in your component.

 <button type="button" class="btn btn-default upload-placeholder">   
	<i class="far fa-3x fa-image"></i>
    <input type="file" ref="file" accept="image/*" @change="upload()">
</button>

methods : {
  //no function called upload
}

It’s simple but very easy to get this error and don’t know where it is.

#vue #vuejs #javascript