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 attribute specifies the HTTP method (GET, POST) used to submit the form-data?
action method value<form action="script.php" method="post"> ... </form>
Which CSS property allows to add shadow to boxes?
background-image box-shadow border-radius#id {
background-color: #bbfeda;
box-shadow: 11px 11px 5px #7878da;
}Which function removes the first element from an array?
pop() push() shift()var fruits = ["apple", "apricot", "banana"];
fruits.shift();
alert(fruits.length); // 2
Indicate the function that can be used to check if a PHP extension is instaled.
function() filetype() extension_loaded()if(extension_loaded("PDO") === true) echo "PDO is available."