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
What attribute makes a radio button or checkbox input selected?
checked="checked" selected="selected" disabled="disabled"<input type="checkbox" name="a_name" value="value" checked="checked" />
What CSS value scales the background image to the largest size contained within the element?
repeat-x contain linear-gradient#id {
background:url("path_to_image.png");
background-size:contain;
background-repeat:no-repeat;
}What operator is used to determine the rest of the division of two numbers?
% * /var rest8_7 = 8 % 7;
alert(rest8_7);
Indicate the PHP function that rounds a number up to the next highest integer.
floor() ceil() abs()$nr = ceil(3.5);
echo $nr; // 4