ts-transformer-log-position

A configurable Typescript AST transformer that injects the position of a log statement from the original source file into the respective log message at build time, allowing you to trace back log messages without emitting, exposing or requiring source maps.

Usage

1. Use a compiler that allows you to use transformers (such as ts-patch)
2. Install the package npm i --save-dev @bitpatty/ts-transformer-log-position
3. For ts-patch users: Add the transformer to your tsconfig.json:

{
  "compilerOptions": {
    "plugins": [
      {
        "transform": "@bitpatty/ts-transformer-log-position"
        // Additional transformer configuration can be applied here
      }
    ]
  }
}

If you use a different compiler than ts-patch, refer to the respective documentation on how to apply transformers.

Sample

console.log(); // input
console.log('[src/sample.ts:0:0]'); // output

console.log(foo); // input
console.log('[src/sample.ts:3:0]', foo); // output

Ignoring lines

Individual lines can be ignored by adding @ts-transformer-log-position ignore to the line before the log statement. To ignore an entire file add @ts-transformer-log-position disable on the top of the file (before any imports or logic).

// @ts-transformer-log-position disable
console.log('foo'); // will be ignored
console.log('foo'); // will be ignored

/* Some other comments */
// ...

// @ts-transformer-log-position disable
console.log('foo'); // will be ignored
console.log('foo'); // will be ignored

console.log('foo'); // will NOT be ignored
// @ts-transformer-log-position ignore
console.log('foo'); // will be ignored
console.log('foo'); // will NOT be ignored

Configuration

The plugin provides the configuration options below.

split

Whether to split the arguments in the log statement. Defaults to true.

console.log('[src/sample.ts:0:0]', foo); // split: true
console.log('[src/sample.ts:1:0] ' + `${foo}`); // split: false

templateString

The template string for the log prefix. Defaults to "[{projectFilePath}:{line}:{character}]".

The following placeholders are available:

• absoluteFilePath: The absolute path to the file
• fileName: The name of the file
• projectFilePath: The absolute path to the file from the project root. The project root is auto-detected, but can be modified via the projectRoot option

console.log('[/workspace/src/sample.ts:0:0]', foo); // templateString: "[{absoluteFilePath}:{line}:{character}]"
console.log('src/sample.ts, line 1', foo); // templateString: "{projectFilePath}, line {line}"
console.log('sample.ts, line 1', foo); // templateString: "{fileName}, line {line}"

expressions

The pattern of the call expression that should be matched against to apply the transformer. Defaults to: ['console.log', 'console.warn', 'console.debug', 'console.error', 'console.trace']

// expressions: "Logger.log"
Logger.log('[src/sample.ts:1:0]', foo);
console.log(foo); // not modified

// expressions: ["Logger.log", "console.log"]
Logger.log('[src/sample.ts:5:0]', foo);
console.log('[src/sample.ts:6:0]', foo);

incrementLineNumber / incrementCharNumber

Adds +1 to each line / character number to match the numbering of common editors (starting from 1 instead of 0). Defaults to false.

argsToJson / stringArgsToJson

If argsToJson is true, the log arguments are wrapped in a JSON stringify. It omits strings and template expressions unless stringArgsToJson is true. Defaults to false / false.

Examples:

// argsToJson: true

// in
console.log(foo);
// out
console.log('[src/sample.ts:0:0] ' + JSON.stringify(foo));

// in
console.log(1 + 1);
// out
console.log('[src/sample.ts:0:0] ' + JSON.stringify(1 + 1));

// in
console.log(...foo);
// out
console.log(
  '[src/sample.ts:0:0] ',
  ...foo.map((__ttlp__v_0) => JSON.stringify(__ttlp__v_0)),
);

// in
console.log(a, b, c);
// out
console.log(
  '[src/sample.ts:0:0] ' + JSON.stringify(a),
  JSON.stringify(b),
  JSON.stringify(c),
);