A watcher allows you to "watch" a property of the component data, and run a function when that property value changes.
In the watch object add a method with the same name as the property data you want to "watch".
Syntax:
var vm = new Vue({
el: 'css_selector',
data: {
prop_name: 'value'
}.
watch: {
prop_name: function(newVal, oldVal{
//code and value to return
}
}
});
The function assigned to watch.prop_name can optionally accept 2 parameters. The first is the new property value (newVal). The second is the old property value.
Here is a practical example with the watch property in vue.js. Add the diameter of a circle into an input field, then it is displayed the perimeter and area:
<div id='demo'>
Diameter circle: <input type='number' value='0' v-model='diameter'/><br>
Perimeter: {{perimeter}}<br>
Area: {{area}}
</div>
<script>
var vm = new Vue({
el:'#demo',
data: {
diameter: 0,
perimeter:0,
area:0
},
watch: {
diameter: function(val){
this.perimeter = 3.14*val;
this.area = 3.14*(val*val)/4;
}
}
});
</script>
Daily Test with Code Example
HTML
CSS
JavaScript
PHP-MySQL
Which tag can be used to create input text field in web page?
<form> <input> <div><input type="text" name="a_name" value="val" />
Which CSS property displays the text in a small-caps font?
display font-variant font-styleh3 {
font-variant: small-caps;
}What instruction displays a notice box with a message inside it, in JavaScript?
for() Date() alert()var msg = "Visit CoursesWeb.net";
alert(msg);
Indicate the PHP code used to get the users IP.
$_SERVER["HTTP_USER_AGENT"] $_SERVER["REMOTE_ADDR"] $_GET[]$ip = $_SERVER["REMOTE_ADDR"];
echo $ip;