Passing boolean Vue prop value in HTML

To use a Boolean type as a prop, you have to use v:bind

<Header v-bind:have-banner="true" page-title="Home">

or using a short syntax

<Header :have-banner="true" page-title="Home">

If passing in JS keywords such as boolean values or references to variables, you will need to use v-bind (or :), i.e.:

<Header v-bind:have-banner="true" page-title="Home">

This will have the effect of binding the boolean true to the prop, not a "true" string. If you are not using v-bind, the haveBanner prop will always be truthy because it is a string of non-zero length, no matter if you assign "true" or "false" to it.

Friendly hint: HTML tags are not case-sensitive, so you might want to use custom-header or my-header-component instead of Header:

<custom-header v-bind:have-banner="true" page-title="Home">

See proof-of-concept:

Vue.component('custom-header', {
  template: '#customHeader',
  props: {
    haveBanner: Boolean,
    pageTitle: String
  }
});

new Vue({
  el: '#app'
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.15/vue.min.js"></script>

<div id="app">
  <custom-header v-bind:have-banner="true" page-title="Home"></custom-header>
  <custom-header v-bind:have-banner="false" page-title="Home"></custom-header>
</div>
 
<script type="text/x-template" id="customHeader">
    <header>
        <div v-if="haveBanner">
          <code>haveBanner</code> is true!
        </div>
        <div v-else>
          <code>haveBanner</code> is false!
        </div>
    </header>
</script>

Pro tip: Use : shorthands to make your template more readable, i.e.:

<custom-header :have-banner="true" page-title="Home">