VueJS TypeError: Cannot read property 'className' of undefined

Question

I'm trying to build a menu, highlight the current tab/page the user is on, add a color class, and use JavaScript to update the active link. This is my template:

<div class="w3-bar w3-black">
  <button
    class="w3-bar-item w3-button tablink w3-red"
    onclick="openCity(event,'London')"
  >
    London
  </button>
  <button
    class="w3-bar-item w3-button tablink"
    onclick="openCity(event,'Paris')"
  >
    Paris
  </button>
  <button
    class="w3-bar-item w3-button tablink"
    onclick="openCity(event,'Tokyo')"
  >
    Tokyo
  </button>
</div>

<div id="London" class="w3-container w3-border city">
  <h2>London</h2>
  <p>London is the capital city of England.</p>
</div>

<div id="Paris" class="w3-container w3-border city" style="display:none">
  <h2>Paris</h2>
  <p>Paris is the capital of France.</p>
</div>

<div id="Tokyo" class="w3-container w3-border city" style="display:none">
  <h2>Tokyo</h2>
  <p>Tokyo is the capital of Japan.</p>
</div>

And I have this javascript code in 'methods':

methods: {
    openCity: function(evt, cityName) {
      var i, x, tablinks;
      x = document.getElementsByClassName("city");
      for (i = 0; i < x.length; i++) {
        x[i].style.display = "none";
      }
      tablinks = document.getElementsByClassName("tablink");
      for (i = 0; i < x.length; i++) {
        tablinks[i].className = tablinks[i].className.replace(" w3-red", "");
      }
      document.getElementById(cityName).style.display = "block";
      evt.currentTarget.className += " w3-red";
    }
  }

But I got this error in console: 'TypeError: Cannot read property 'className' of undefined' and the button it doesn't highlight it. Hope you can help me, thanks!

What className is undefined? tablinks[i].classNam or evt.currentTarget.className? — Naomi Messing
– Naomi Messing, Commented Jul 19, 2020 at 14:25

AlekseyHoffman · Accepted Answer · 2020-07-19 15:06:06Z

2

You are passing event instead of $event, I think this is why it's not defined. Also you have a lot of unnecessary code. I cleaned it up, try now:

HTML

<div class="w3-bar w3-black">
  <button
    v-for="city in cities"
    class="w3-bar-item w3-button tablink"
    @click="openCity($event, city)"
    :class="{ 
      'w3-red': city.name === selectedCity,
      'w3-black': city.name !== selectedCity 
    }"
  >
    {{city.name}}
  </button>
</div>

<div 
  v-for="city in cities" 
  :id="city.name" 
  class="w3-container w3-border city"
  :class="{ 
    'visible': city.name === selectedCity,
    'hidden': city.name !== selectedCity 
  }"
 >
  <h2>{{city.name}}</h2>
  <p>{{city.description}}</p>
</div>

script

data () {
  return {
    selectedCity: 'London',
    cities: [
      { 
        name: 'London', 
        description: 'London is the capital city of England'
      },
      { 
        name: 'Paris', 
        description: 'Paris is the capital of France',
      },
      { 
        name: 'Tokyo', 
        description: 'Tokyo is the capital of Japan',
      }
    ] 
  }
},
methods: {
  openCity (event, city) {
    this.selectedCity = city.name
  }
}

styles

.hidden {
  display: none
}

.visible {
  display: block
}

Method 2

If you don't want to use CSS classes to hide the content, you can just use v-show and only the selected city will be shown city.name === selectedCity:

<div 
  v-for="city in cities" 
  v-show="city.name === selectedCity"
  :id="city.name" 
  class="w3-container w3-border city"
 >
  <h2>{{city.name}}</h2>
  <p>{{city.description}}</p>
</div>

edited Jul 19, 2020 at 15:06

answered Jul 19, 2020 at 14:25

AlekseyHoffman

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1 Comment

AlekseyHoffman Over a year ago

@NuzzeSicK glad I could help :). I updated the code again, take a look, I made it more flexible. This way it will be much easier to work with when you have more data.

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