...
In order to calculate the correct coverage, Sealights require the column information on top of the line information. in order to achieve that, please make sure you have set the following, depending on your build tool:
Webpack
Set In your webpack.config.js configuration file, set the devtool property to devtool: ‘source-map' or devtool: ‘inline-source-map'.
If you don’t want to change your project configuration, the corresponding webpack-cli commands will be --devtool 'source-map' or --devtool : 'inline-source-map'.
More details are available as part of the official Webpack documentation: https://webpack.js.org/configuration/devtool/ or https://webpack.js.org/api/cli/#flags
Typescript (tsc)
Add the relevant compiler option --sourceMap or --inlineSourceMap to the command line or to your tsconfig.json
...