Introduction to filter functions in Vue documentation

Vue is a popular JavaScript framework that provides developers with very powerful tools to build interactive web applications. One of the commonly used functions in the Vue framework is the filter function. In this article, we will introduce filter functions in Vue documentation and how to use them.

1. What is Vue filter function?

The filter function in Vue is a function used to format text. It can process the data we pass to the template and then output the processed results. Normally, we can use filter functions to format dates, numbers, strings, arrays, etc.

2. How to use the Vue filter function

To use the Vue filter function, we need to use its global registration method or local registration method. The following describes how to use these two methods:

1. Globally register a filter function

You can register a filter function globally through the Vue.filter() function. For example:

Vue.filter('capitalize', function(value) {
  if (!value) return ''
  value = value.toString()
  return value.charAt(0).toUpperCase() + value.slice(1)
})

The above code registers a filter function named capitalize, which accepts a string type parameter, then capitalizes its first letter, and returns the processed result.

2. Local registration filter function

In addition to global registration, we can also use local registration to register filter functions in specific components. For example:

Vue.component('my-component', {
  filters: {
    capitalize: function(value) {
      if (!value) return ''
      value = value.toString()
      return value.charAt(0).toUpperCase() + value.slice(1)
    }
  },
  template: '<div>{{ message | capitalize }}</div>',
  data: function() {
    return {
      message: 'hello world'
    }
  }
})

The above code defines a component named my-component, and defines a filter function named capitalize in the filters option of the component. Finally, the $message variable is used in the component's template, as well as the capitalize filter function.

3. Purpose of Vue filter function

Vue’s filter function can be used for many purposes. Here are a few commonly used examples:

1. Formatting Date

When developing with Vue, we usually need to convert the date into an easy-to-read format. At this time, we can use the filter function to complete. For example:

Vue.filter('formatDate', function(value) {
  const date = new Date(value)
  return date.toLocaleDateString()
})

The above code registers a filter function named formatDate, which accepts a timestamp type parameter and converts it into a local date string, such as "2022/6/15".

2. Number formatting

In some scenarios, we need to format numeric data, such as adding thousands separators, retaining decimal points, etc. This can be done using the filter function. For example:

Vue.filter('formatNumber', function(value) {
  return value.toString().replace(/B(?=(d{3})+(?!d))/g, ',')
})

The above code registers a filter function named formatNumber, which accepts a numeric type parameter and adds a comma to its thousands digit, such as "1,000,000".

3. String interception

In some scenarios, we need to intercept strings, such as intercepting the number of characters, adding ellipses, etc. This can be done using the filter function. For example:

Vue.filter('truncate', function(value, maxLength = 150) {
  if (value.length <= maxLength) {
    return value
  }
  return value.slice(0, maxLength) + '...'
})

The above code registers a filter function named truncate, which accepts a string type parameter and intercepts it to a certain length. If it exceeds, an ellipsis is added.

Conclusion:

The Vue filter function is a very practical part of the Vue framework, which allows us to quickly perform data formatting operations. The above introduces the definition and use of Vue filter functions, and gives several commonly used examples. With these basic knowledge and skills, we can complete formatting operations more efficiently in Vue development.

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