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
Click on the HTML tag which creates an horizontal line in web page.
<br /> <em> <hr />Some content ...
<hr />
Content under line ...
Which CSS property defines the text color?
font-style font-variant colorh2 {
color: #cbdafb;
}Click on the function which searches if a character, or text exists in a string.
indexOf() toString() split()var str = "Web courses - http://CoursesWeb.net/";
if(str.indexOf("http://") == -1) alert("http:// isn`t in string");
else alert("http:// is in string");Which function splits a string into an array of strings based on a separator?
array_merge() explode() implode()$str = "apple,banana,melon,pear";
$arr = explode(",", $str);
var_export($arr); // array (0=>"apple", 1=>"banana", 2=>"melon", 3=>"pear")