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 adds an image in web page?
<div> <img> <span><img src="http://coursesweb.net/imgs/webcourses.gif" width="191" height="63" alt="Courses-Web" />
Which of these CSS codes displays the text oblique?
font-style: italic; text-decoration: underline; font-weight: 500;#id {
font-style: italic;
}Click on the jQuery function used to hide with animation a HTML element.
click() hide() show()$(document).ready(function() {
$(".a_class").click(function(){ $(this).hide("slow"); });
});Click on the correctly defined function in PHP.
fname function() {} function fname() {} function $fname() {};function fname($a, $b) {
echo $a * $b;
}