Cannot read property replace of null method parameter - laravel

Question

I started messing around with Vue.js earlier this week.
So far I created a list of MTG(a TCG) cards. The data comes from the database through an Ajax request. This all works like a charm.
What i want to do next is replace the string that contains the costs of a card e.g. something like '{1}{U}{G}' with images for the corresponding tag.
HTML:
<div v-for="(cards, key) in mainBoard" class="">
<table class="table">
<tr>
<th colspan="5">#{{ key }}</th>
</tr>
<tr>
<th>#</th>
<th>Name</th>
<th>ManaCost</th>
#if($deck->enableCommander())
<th>Commander</th>
#else
<th></th>
#endif
<th>Actions</th>
</tr>
<tr v-for="card in cards">
<td>#{{card.pivot.quantity}}</td>
<td>#{{card.name}}</td>s
<td v-html="replaceManaSymbols(card)"></td>
#if($deck->enableCommander())
<td>
<span v-if="card.pivot.commander" #click="preformMethod(card, 'removeCommander', $event)"><i class="fa fa-flag"></i></span>
<span v-else #click="preformMethod(card,'assignCommander', $event)"><i class="far fa-flag"></i></span>
</td>
#else
<td> </td>
#endif
<td>
<button #click="preformMethod(card,'removeCardFromDeck', $event)"><i class="fa fa-times-circle"></i></button>
<button #click="preformMethod(card,'plusCardInDeck', $event)"><i class="fa fa-plus-circle"></i></button>
<button #click="preformMethod(card,'minusCardInDeck', $event)"><i class="fa fa-minus-circle"></i></button>
</td>
</tr>
</table>
</div>
Vue.js
new Vue({
el: '#Itemlist',
data: {
mainBoard: [],
sideBoard: [],
},
methods:{
preformMethod(card, url){
var self = this;
var varData = {
slug: '{{ $deck->slug }}',
card: card.id,
board: card.pivot.mainboard
};
$.ajax({
url: '/vue/'+url,
data: varData,
method: 'GET',
success: function (data) {
self.mainBoard = data.mainBoard;
self.sideBoard = data.sideBoard;
},
error: function (error) {
console.log(error);
}
});
},
replaceManaSymbols(card){
var mc = card.manaCost;
var dump = mc.replace(/([}])/g, '},').split(',');
var html = '';
/**
* replace each tag with an image
*/
return html;
}
},
mounted(){
var self = this;
var varData = {
slug: '{{ $deck->slug }}'
};
$.ajax({
url: '/vue/getDeckList',
data: varData,
method: 'GET',
success: function (data) {
self.mainBoard = data.mainBoard;
self.sideBoard = data.sideBoard;
},
error: function (error) {
console.log(error);
}
});
}
})
I pass the card as a parameter to the replaceManaSymbols method. I can console.log the contents of mana without any issue. But as soon as a want to modify the string Vue throws the error TypeError: Cannot read property 'toLowerCase/split/replace' of null. I'm not really sure what's going wrong. Any idea's?

Answer 1

As a rule of thumb, you shouldn't use methods on the display side. Keep them for the update side - processing changes back into a store and such. Methods aren't reactive - they need to be called. You want your display to automatically reflect some underlying data, so you should use computed.
You should also avoid using v-html, because you end up with markup outside your templates, and that markup is static. It's not totally clear to me what will be in v-html, but you should try and keep markup in your template, and inject values using data, props or computed. Hope this helps!
If you want a div with some text that magically turns into an image tag, this could be a good use for <component :is>.