你要先有一个react项目

1. npm install -g create-react-app
2. create-react-app my-react （创建文件名为my-react的项目）
3. cd my-react （进入根目录）
4. npm start （编译程序运行my-react这个项目）
5. 进入（http://localhost:3000/）

安装less

1. npm i less less-loader --save
2. 然后使用命令npm run eject使config文件夹 ‘暴露’ 出来
3. 找到webpack.config.js文件，搜索 sass然后就会发现这段代码

// style files regexes
const cssRegex = /\.css$/;
const cssModuleRegex = /\.module\.css$/;
const sassRegex = /\.(scss|sass)$/;
const sassModuleRegex = /\.module\.(scss|sass)$/;

4. 然后再这段代码下面配置以下代码

// 添加 less 解析规则
const lessRegex = /\.less$/;
const lessModuleRegex = /\.module\.less$/;

5. 再找到以下代码

// Adds support for CSS Modules (https://github.com/css-modules/css-modules)
// using the extension .module.css
{
    test: cssModuleRegex,
    use: getStyleLoaders({
        importLoaders: 1,
        sourceMap: isEnvProduction
            ? shouldUseSourceMap
            : isEnvDevelopment,
        modules: {
            getLocalIdent: getCSSModuleLocalIdent,
        },
    }),
},
// Opt-in support for SASS (using .scss or .sass extensions).
// By default we support SASS Modules with the
// extensions .module.scss or .module.sass
{
    test: sassRegex,
    exclude: sassModuleRegex,
    use: getStyleLoaders(
        {
            importLoaders: 3,
            sourceMap: isEnvProduction
                ? shouldUseSourceMap
                : isEnvDevelopment,
        },
        'sass-loader'
    ),
    // Don't consider CSS imports dead code even if the
    // containing package claims to have no side effects.
    // Remove this when webpack adds a warning or an error for this.
    // See https://github.com/webpack/webpack/issues/6571
    sideEffects: true,
},
// Adds support for CSS Modules, but using SASS
// using the extension .module.scss or .module.sass
{
    test: sassModuleRegex,
    use: getStyleLoaders(
        {
            importLoaders: 3,
            sourceMap: isEnvProduction
                ? shouldUseSourceMap
                : isEnvDevelopment,
            modules: {
                getLocalIdent: getCSSModuleLocalIdent,
            },
        },
        'sass-loader'
    ),
},

6. 把这段中关于Sass的配置复制下来，把关键字换成less（sass ==> less）

//less配置    可以直接复制上面的sass配置之后改成less就行
{
    test: lessRegex,
    exclude: lessModuleRegex,
    use: getStyleLoaders(
        {
            importLoaders: 3,
            sourceMap: isEnvProduction
                ? shouldUseSourceMap
                : isEnvDevelopment,
        },
        'less-loader'
    ),
    // Don't consider CSS imports dead code even if the
    // containing package claims to have no side effects.
    // Remove this when webpack adds a warning or an error for this.
    // See https://github.com/webpack/webpack/issues/6571
    sideEffects: true,
},
{
    test: lessModuleRegex,
    use: getStyleLoaders(
        {
            importLoaders: 3,
            sourceMap: isEnvProduction
                ? shouldUseSourceMap
                : isEnvDevelopment,
            modules: {
                getLocalIdent: getCSSModuleLocalIdent,
            },
        },
        'less-loader'
    ),
},

7. 保存重启项目就好了哦！