The technical principles of the PostCSS framework of the POSTCSS framework
The technical principles of the postcss framework of the postcss framework
In modern web development, the style table is an important part of building a user interface.PostCSS is a powerful and flexible CSS processing tool that can help developers improve the writing and maintenance efficiency of style tables.This article will analyze the technical principles of the POSTCSS framework and provide some application practice to help developers better understand and apply PostCSS.
# What is postcss?
PostCSS is a plug -in CSS processing tool.It is written in JavaScript and can be transformed and optimized by loading various plug -ins.The core principle of PostCSS is to resolve CSS into abstract syntax trees (AST), then operate and transform AST through a series of plug -ins, and finally turn AST back to CSS.This AST -based processing method allows developers to freely define their required conversion and optimization rules, thereby achieving more flexible and scalable style table processing.
# Postcss's technical principle
## Analysis CSS is an abstract syntax tree
Before dealing with CSS, the CSS needs to be parsed into abstract syntax trees.The analysis process of CSS includes two stages: phrase analysis and grammar analysis.Postcss uses CSS-Tree as the default parser, which can analyze the CSS code into a structured abstract syntax tree.
The following is an example code that uses CSS-Tree to analyze CSS and print AST:
import csstree from 'css-tree';
const css = `
.container {
color: red;
font-size: 14px;
}
`;
const ast = csstree.parse(css);
console.log(csstree.generate(ast));
## plug -in processing and conversion
The core idea of PostCSS is to process and change the abstract syntax tree through plug -ins.Developers can choose the appropriate plug -in according to their needs and configure them as needed.
The following is an example of using the AutoPREFIXER plugin to add browser prefix to CSS:
import postcss from 'postcss';
import autoprefixer from 'autoprefixer';
const css = `
.container {
display: flex;
}
`;
const processedCss = postcss([autoprefixer])
.process(css)
.css;
console.log(processedCss);
In this example, we used the Autoprefixer plug -in to mobilize to `Display: Flex;` This CSS code is added to the browser prefix.Create a postcss processor by using the `postcss ([Autoprefixer])` `and pass the plug -in list to be used, and then process the CSS by calling the` Process` method.Finally, we can obtain the CSS code after processing through the `.css` attribute.
## custom plug -in development
In addition to using existing plug -ins, PostCSS also supports developers custom plug -in to meet specific needs.Developing a postcss plug -in requires a callable function and accepts a `root` parameter, which indicates the resolved abstract syntax tree.
The following is an example of a simple custom plug -in, which is used to convert all CSS selectors into a lowercase:
import postcss from 'postcss';
function toLowerCaseSelectors(root) {
root.walkRules(rule => {
rule.selectors = rule.selectors.map(selector => selector.toLowerCase());
});
}
const css = `
.Container {
color: red;
}
`;
const processedCss = postcss([toLowerCaseSelectors])
.process(css)
.css;
console.log(processedCss);
In this example, we define a custom plug -in called `TOLOWERCASESELECTORS`.It traverses the CSS rules by calling the `root.walkrules` method, and to modify the effect of converting all selectors into lowercase by modifying the` rule.selectors`.
#Postcss's application practice
## style automatically add browser prefix
A common application practice is to automatically add browser prefixes to CSS using the Autoprefixer plug -in.This can ensure the compatibility of the style in the environment of different browsers and reduce the workload of developers to manually add prefixes.
import postcss from 'postcss';
import autoprefixer from 'autoprefixer';
const css = `
.container {
display: flex;
}
`;
const processedCss = postcss([autoprefixer])
.process(css)
.css;
console.log(processedCss);
Through this code, we can automatically add appropriate browser prefixes for `Display: Flex;`.This can ensure that the style can be displayed normally in various browsers when using the Flexbox layout.
## CSS style optimization and compression
PostCSS can also optimize CSS style and compress with some plug -in to improve the performance of webpage loading.For example, CSSNANO is a commonly used CSS compressed plug -in, which can remove comments, spaces and useless style declarations.
import postcss from 'postcss';
import cssnano from 'cssnano';
const css = `
/ * Note */
.container {
color: red;
}
`;
const processedCss = postcss([cssnano])
.process(css)
.css;
console.log(processedCss);
By using the CSSNANO plugin, we can remove the annotations in the above example and compress the CSS to reduce the file size of the style table.
# Summarize
PostCSS is a powerful and flexible CSS processing tool, which uses plug -in to transform and optimize the style table.This article introduces the technical principles of PostCSS, including analyzing CSS as abstract syntax trees and plug -in processing.We also provide some common application practices to help developers better understand and apply PostCSS.
I hope that through the introduction of this article, you have a deeper understanding of the technical principles and application practice of PostCSS, and can flexibly use PostCSS to improve efficiency and optimize style tables in daily web development.
