Vuejs Course


Vue.js contains a set of core directives to show or hide elements based on conditions: v-if, v-else, v-else-if and v-show.

The v-if directive

The v-if directive adds or removes DOM elements based on the value true or false of the given expression.

- Syntax:
<div v-if='can_add'>content</div>
If the "can_add" is True that element is added in HTML DOM, if it is False the element is deleted.

- Example:
<div id='demo'>
 <div v-if='can_add'>Forgiveness is healing.</div>
 Click to <button @click='addRem'>Add/Remove</button>
</div>

<script>
var vm = new Vue({
 el: '#demo',
 data:{ can_add:false },
 methods:{
 addRem:function(){
 this.can_add = !this.can_add; //switch true /false
 }
 }
});
</script>

Conditional Groups with v-if on <template>

The v-if directive can only be attached to a single element, but you can also control multiple elements with a single v-if. To do this, wrap all the elements in a <template> element.

- Example:
<div id='demo'>
 <template v-if='can_add'>
 <h4>Forgiveness is healing.</h4>
 <h4>Healing is forgiveness.</h4>
 </template>
 Click to <button @click='addRem'>Add/Remove</button>
</div>

<script>
var vm = new Vue({
 el: '#demo',
 data:{ can_add:false },
 methods:{
 addRem:function(){
 this.can_add = !this.can_add; //switch true /false
 }
 }
});
</script>

The v-else directive

The v-else directive is used to add content only when the expression adjacent v-if resolves to false.
v-else does not need a value passed in to it. But it must be in an element that comes immediately after an element containing v-if or v-else-if directives.

- Example:
<div id='demo'>
 <h4 v-if='can_add'>This is in tag with v-if.</h4>
 <h4 v-else>This content is from v-else.</h4>
 Click to <button @click='addRem'>Toggle message</button>
</div>

<script>
var vm = new Vue({
 el: '#demo',
 data:{ can_add:false },
 methods:{
 addRem:function(){
 this.can_add = !this.can_add; //switch true /false
 }
 }
});
</script>

The v-else-if directive

The v-else-if can be used when we need more than two options to be checked.
A v-else-if element must immediately follow a v-if or a v-else-if element.

- Example:
<div id='demo'>
 <h4 v-if='rest ==1'>This is in the tag with v-if, rest ={{rest}}.</h4>
 <h4 v-else-if='rest ==2'>This is from v-else-if, rest ={{rest}}.</h4>
 <h4 v-else>This content is from v-else, rest not 1 or 2; rest ={{rest}}.</h4>
 Click to <button @click='addRem'>Alternate elements</button>
</div>

<script>
var vm = new Vue({
 el: '#demo',
 data:{ rest:0, nr:0 },
 methods:{
 addRem:function(){
 this.nr++;
 this.rest = this.nr %3;
 }
 }
});
</script>

The v-show directive

The effect of v-show directive is similar to v-if, it can be used to hide and show an element based on an expression.
Here is the differences between the two:

- Example:
<div id='demo'>
 <h4 v-show='can_show'>Observing leads to healing.</h4>
 Click to <button @click='addRem'>Show /Hide</button>
</div>

<script>
var vm = new Vue({
 el: '#demo',
 data:{ can_show:false },
 methods:{
 addRem:function(){
 this.can_show = !this.can_show; //switch true /false
 }
 }
});
</script>

The v-show has a performance advantage if the elements are switched on and off frequently, while the v-if has the advantage when it comes to initial render time.

Daily Test with Code Example

HTML
CSS
JavaScript
PHP-MySQL
What attribute makes the input text box to not be modified by the user?
checked="checked" readonly="readonly" disabled="disabled"
<input type="text" value="fixed-value" readonly="readonly" name="a_name" />
What CSS property allows you to create rounded corners in your webpage design?
background-size border-size border-radius
.class {
  border:2px solid blue;
  border-radius:1.2em;
}
What instruction displays a confirmation dialog box to the viewer, who must then click OK or Cancel to proceed?
indexOf() confirm() prompt()
var ques = window.confirm("The result of 0+0 is 0?");
if (ques) alert("Corect");
else alert("Incorrect");
Indicate the PHP function that returns the lowest number of the parameter values.
floor() ceil() min()
$min_nr = min(12, 8, 25, 13);
echo $min_nr;        // 8
Conditional Directives v-if, v-else, v-show

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