Enable inline javascript in LESS

If you're using the lessc the cli interface then you just need --js on the end.

lessc --js ./styles/theme.less ./styles/theme.css

I had same problem, I use webpack with less loader, I needed to add javascript option in less loader config:

{
        test: /\.less$/,
        use: [{
            loader: "style-loader"
        }, {
            loader: "css-loader"
        }, {
            loader: "less-loader",
            options: {
                javascriptEnabled: true
            }
        }]
}

I found in the sourcecode of less compiler: https://github.com/less/less.js/blob/3.x/bin/lessc

that they parse js less option in this way:

        case 'js':
            options.javascriptEnabled = true;
            break;
        case 'no-js':
            console.error('The "--no-js" argument is deprecated, as inline JavaScript ' + 
                'is disabled by default. Use "--js" to enable inline JavaScript (not recommended).');
            break;

So you should probably use '--js' in a static compilation ( command line ) or 'javascriptEnabled: true' in a dynamic compilation ( like webpack loader ) to enable javascript.

Just to update the accepted answer,

From 3.11.1, if you use just options, it will throw :

ValidationError: Invalid options object. Less Loader has been initialized using an options object that does not match the API schema. - options has an unknown property 'javascriptEnabled'. These properties are valid: object { lessOptions?, prependData?, appendData?, sourceMap?, implementation? }

In [email protected], it's not just options that should be used, but lessOptions like this :

{
    test: /\.less$/,
    use: [{
        loader: "style-loader"
    }, {
        loader: "css-loader"
    }, {
        loader: "less-loader",
        options: {
          lessOptions: {
             javascriptEnabled: true
          }
        }
    }]
}

Updated: May 2020

For less-loader version 6.1.0^.

In "less-loader" version 6.1.0^ they made breaking changes to the loader that, if you used something like Ant Design (or other LESS and JS loaders) you would nomally add the javascriptEnabled: true flag to the "options" object in your Webpack configuration.

In version 6.1.0^ this was change to be placed in the lessOptions object under the options configuration for the less loader. Here is the solution I used, that works for my Webpack configuration bundle.

module: { rules: [{
    test: /\.less$/,
    use: [
        { loader: "style-loader" },
        { loader: "css-loader" },
        {
            loader: "less-loader",
            options: {
                lessOptions: {
                    javascriptEnabled: true,
                }
            }
        }
    ]
}]}

Notice that the javascriptEnabled flag is not under the top-level options object, but it, instead, under the lessOptions sub-object. That is the latest updated standard as of less-loader version 6.1.0^.