The core of writing a Babel plug-in is to understand and operate AST. 1. First understand the structured representation of the code through AST Explorer and find the node type to be modified; 2. The basic structure of the plug-in is to return an object containing a visitor and define operations on a specific node; 3. Use the path.node or path method to modify node properties or replace nodes; 4. Debug plug-in effects in real time through project testing, Babel plugin-tester or AST Explorer; 5. Pay attention to avoiding side effects, use @babel/types to create nodes, handle Scope conflicts, generate unique variable names, and support plug-in configuration options. Once you master these steps, writing the Babel plugin will become clear and easy to understand.
Writing a Babel plug-in is actually not that mysterious, mainly to understand the structure and processing of AST (abstract syntax tree). If you have used Babel and know that it can convert code, you can try writing a plugin yourself to customize your JavaScript conversion logic.
Understanding AST is the first step
The core of the Babel plug-in is to operate AST. AST is a structured representation of the code, such as a function call, variable declaration, if statement, etc., which will be converted into a specific node object. You don't need to write AST yourself, but access, modify, and replace these nodes through the API provided by Babel.
To give the simplest example: you want to replace all console.log with a custom log function. Then all you have to do is find the node of type CallExpression , and then determine that its callee.object is console and callee.property is log , and then replace it with the expression you want.
You can use AST Explorer to view the AST structure corresponding to the code, which is very helpful for understanding how to write plugins.
Start with the simplest plugin structure
A Babel plugin is essentially a function that returns an object, which contains an accessor, which defines the type of node you want to operate on.
The basic structure is as follows:
module.exports = function () {
return {
Visitor: {
// Define the node type to be processed here},
};
}; Suppose you want to change all var declarations let , you can listen to VariableDeclaration node:
Visitor: {
VariableDeclaration(path) {
if (path.node.kind === 'var') {
path.node.kind = 'let';
}
}
} The key here is to get the current node through path.node and modify its properties. Remember, path provides more operation methods, such as replaceWith , remove , insertBefore , etc.
Plugin debugging and testing are important
After writing the plugin, you have to test whether it takes effect. There are several ways to:
- Install the plugin in the project, run Babel translation, and see if the output is as expected
- Writing unit tests using Babel's plugin-tester
- Load your plug-in directly in AST Explorer to see the effects in real time
Printing AST is a good habit when debugging. For example, add a sentence console.log(path.node) to the accessor to quickly view the node structure.
In addition, the order of plugins is also critical. The execution order of Babel plug-ins is in configuration order. If your plug-in depends on the conversion result of another plug-in, you may need to adjust the order.
Some tips in practical applications
- Avoid too much modification of AST : Try to modify only necessary nodes to avoid side effects
- Use @babel/types tool : For example, when creating a new node, it is safer to use
t.identifier('let')than to write objects manually - Note Scope problem : If you want to add variables or functions, to ensure that there is no naming conflict, you can use
path.scope.generateUidIdentifierto generate unique variable names - Support option configuration : Plugin can accept parameters, such as
function myPlugin({ types: t }, options), which is more flexible
Basically that's it. Writing a Babel plug-in may feel a bit abstract at first, but once you become familiar with the AST structure and accessor mode, you will find that it is actually quite straightforward.
The above is the detailed content of Building Custom JavaScript Babel Plugins. For more information, please follow other related articles on the PHP Chinese website!
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