technology-blog 第 9 题：简单实现项目代码按需加载，例如import { Button } from 'antd'，打包的时候只打包button

原理很简单，就是将

import { Select, Pagination, Button } from 'xxx-ui';

通过babel转化成

import Button from `xxx-ui/src/components/ui-base/Button/Button`;
import Pagination from `xxx-ui/src/components/ui-base/Pagination/Pagination`;
import Select from `xxx-ui/src/components/ui-base/Select/Select`;

自定义拓展一个babel插件，代码如下：

visitor: {
	ImportDeclaration (path, { opts }) {
	    const specifiers = path.node.specifiers;
	    const source = path.node.source;

            // 判断传入的配置参数是否是数组形式
	    if (Array.isArray(opts)) {
	        opts.forEach(opt => {
	            assert(opt.libraryName, 'libraryName should be provided');
	        });
	        if (!opts.find(opt => opt.libraryName === source.value)) return;
	    } else {
	        assert(opts.libraryName, 'libraryName should be provided');
	        if (opts.libraryName !== source.value) return;
	    }

	    const opt = Array.isArray(opts) ? opts.find(opt => opt.libraryName === source.value) : opts;
	    opt.camel2UnderlineComponentName = typeof opt.camel2UnderlineComponentName === 'undefined'
	        ? false
	        : opt.camel2UnderlineComponentName;
	    opt.camel2DashComponentName = typeof opt.camel2DashComponentName === 'undefined'
	        ? false
	        : opt.camel2DashComponentName;

	    if (!types.isImportDefaultSpecifier(specifiers[0]) && !types.isImportNamespaceSpecifier(specifiers[0])) {
	        // 遍历specifiers生成转换后的ImportDeclaration节点数组
    		const declarations = specifiers.map((specifier) => {
	            // 转换组件名称
                    const transformedSourceName = opt.camel2UnderlineComponentName
                	? camel2Underline(specifier.imported.name)
                	: opt.camel2DashComponentName
            		    ? camel2Dash(specifier.imported.name)
            		    : specifier.imported.name;
    		    // 利用自定义的customSourceFunc生成绝对路径，然后创建新的ImportDeclaration节点
                    return types.ImportDeclaration([types.ImportDefaultSpecifier(specifier.local)],
                	types.StringLiteral(opt.customSourceFunc(transformedSourceName)));
                });
                // 将当前节点替换成新建的ImportDeclaration节点组
    		path.replaceWithMultiple(declarations);
    	}
    }
}