版本说明：本文档针对vue-cli2

一.安装less

npm i less less-loader --save-dev

二.设置less变量到全局

// 1.安装sass-resources-loader
npm install sass-resources-loader --save-dev

// 2.配置build/utils.js，找到exports.cssLoaders函数，如下
exports.cssLoaders = function (options) {
  options = options || {}

  const cssLoader = {
    loader: 'css-loader',
    options: {
      sourceMap: options.sourceMap
    }
  }

  const postcssLoader = {
    loader: 'postcss-loader',
    options: {
      sourceMap: options.sourceMap
    }
  }

  // 此处添加配置

  // generate loader string to be used with extract text plugin
  function generateLoaders (loader, loaderOptions) {
    const loaders = options.usePostCSS ? [cssLoader, postcssLoader] : [cssLoader]

    if (loader) {
      loaders.push({
        loader: loader + '-loader',
        options: Object.assign({}, loaderOptions, {
          sourceMap: options.sourceMap
        })
      })
    }

    // Extract CSS when that option is specified
    // (which is the case during production build)
    if (options.extract) {
      return ExtractTextPlugin.extract({
        use: loaders,
        fallback: 'vue-style-loader'
      })
    } else {
      return ['vue-style-loader'].concat(loaders)
    }
  }

  // https://vue-loader.vuejs.org/en/configurations/extract-css.html
  return {
    css: generateLoaders(),
    postcss: generateLoaders(),
    less: generateLoaders('less'), // 第二步更改这里
    sass: generateLoaders('sass', { indentedSyntax: true }),
    scss: generateLoaders('sass'),
    stylus: generateLoaders('stylus'),
    styl: generateLoaders('stylus')
  }
}

在上面注释“// 此处添加配置”处添加如下代码：

 // 配置less变量全局
  function lessResourceLoader() {
    var loaders = [
      cssLoader,
      'less-loader',
      {
        loader: 'sass-resources-loader',
        options: {
          resources: [
            path.resolve(__dirname, '../src/assets/style/var.less'), // ../src/assets/style/var.less为你的全局less变量的文件目录
          ]
        }
      }
    ]
    if (options.extract) {
      return ExtractTextPlugin.extract({
        use: loaders,
        fallback: 'vue-style-loader'
      })
    } else {
      return ['vue-style-loader'].concat(loaders)
    }
  }

3.更改exports.cssLoaders函数的return参数，将less: generateLoaders(‘less’)改为 less: lessResourceLoader(‘less’)，如下：

 return {
    css: generateLoaders(),
    postcss: generateLoaders(),
    //  less: generateLoaders('less'), // 更改这里为下面一行
    less: lessResourceLoader('less'),  // lessResourceLoader即第一步添加的函数名
    sass: generateLoaders('sass', { indentedSyntax: true }),
    scss: generateLoaders('sass'),
    stylus: generateLoaders('stylus'),
    styl: generateLoaders('stylus')
  }

经过上面两处更改后，exports.cssLoaders函数如下：

exports.cssLoaders = function (options) {
  options = options || {}

  const cssLoader = {
    loader: 'css-loader',
    options: {
      sourceMap: options.sourceMap
    }
  }

  const postcssLoader = {
    loader: 'postcss-loader',
    options: {
      sourceMap: options.sourceMap
    }
  }

  // 第一步：配置less变量全局
  function lessResourceLoader() {
    var loaders = [
      cssLoader,
      'less-loader',
      {
        loader: 'sass-resources-loader',
        options: {
          resources: [
            path.resolve(__dirname, '../src/assets/style/var.less'), // ../src/assets/style/var.less为你的全局less变量的文件目录
          ]
        }
      }
    ]
    if (options.extract) {
      return ExtractTextPlugin.extract({
        use: loaders,
        fallback: 'vue-style-loader'
      })
    } else {
      return ['vue-style-loader'].concat(loaders)
    }
  }

  // generate loader string to be used with extract text plugin
  function generateLoaders (loader, loaderOptions) {
    const loaders = options.usePostCSS ? [cssLoader, postcssLoader] : [cssLoader]

    if (loader) {
      loaders.push({
        loader: loader + '-loader',
        options: Object.assign({}, loaderOptions, {
          sourceMap: options.sourceMap
        })
      })
    }

    // Extract CSS when that option is specified
    // (which is the case during production build)
    if (options.extract) {
      return ExtractTextPlugin.extract({
        use: loaders,
        fallback: 'vue-style-loader'
      })
    } else {
      return ['vue-style-loader'].concat(loaders)
    }
  }

  // https://vue-loader.vuejs.org/en/configurations/extract-css.html
  return {
    css: generateLoaders(),
    postcss: generateLoaders(),
    // 第二步： less: generateLoaders('less')更改为 less: lessResourceLoader('')
    // less: generateLoaders('less'),
    less: lessResourceLoader(''),
    sass: generateLoaders('sass', { indentedSyntax: true }),
    scss: generateLoaders('sass'),
    stylus: generateLoaders('stylus'),
    styl: generateLoaders('stylus')
  }
}

重启项目即可