How to create a global filter function in Vue documentation

Vue.js is a very popular front-end framework and is widely used in front-end development. Among them, filters are a very important part of Vue.js. They can help developers preprocess data before rendering it to achieve various effects. This article will introduce how to create a global filter function in Vue.js.

The filter in Vue.js is similar to a function, accepting a parameter (usually the data that needs to be filtered) and returning the processed result. A global filter function can be defined via the Vue.filter method to make it available throughout the application. The following is the basic syntax of Vue.filter:

Vue.filter('filterName', function(value) {
  // 处理逻辑
  return processedValue;
});

Among them, 'filterName' is the name of the filter, and value is the data that needs to be filtered. In functions, we can perform various customized operations, such as string replacement, data formatting, etc. Finally, we need to return the processed results.

You can use the defined global filter in the following way:

{{ data | filterName }}

where data is the data that needs to be filtered, and filterName is the name of the defined filter function. The method of use in the template is very simple. You only need to put the data to be filtered after the vertical bar (|) symbol, and then write the name of the filter. It should be noted that filters should be as simple as possible so as not to affect the performance of data binding.

Below we use a specific example to demonstrate how to create and use global filters. Suppose we have a date data and we need to format it in the form of "YYYY-MM-DD". Then we can define the filter as follows:

Vue.filter('formatDate', function(value) {
  var date = new Date(value);
  var year = date.getFullYear();
  var month = date.getMonth() + 1;
  var day = date.getDate();

  // 将数字转为字符串，并在前面补“0”以达到位数的要求
  month = month.toString().padStart(2, '0');
  day = day.toString().padStart(2, '0');

  // 返回格式化之后的日期字符串
  return year + '-' + month + '-' + day;
});

After defining it, we can use it in the template:

<h1>{{ date | formatDate }}</h1>

The effect is to convert the original date format (such as: 1581072000000) to " 2020-02-07" and render it into the page.

In short, using global filters can greatly improve our development efficiency in Vue.js. We can define various filter functions in the global scope and then access them when needed. This achieves the effect of code reuse. At the same time, be careful not to write filter functions that are too bloated and complex to avoid affecting page performance.

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