An Introduction to JavaScript Compile-Time Processing

An Introduction to JavaScript Compile-Time Processing

An Introduction to JavaScript Compile-Time Processing. Babel’s plugin macros and codegen give us a new dimension to manipulate source code at compile time. Babel is a JavaScript transpiler. It enables us to write modern JavaScript that will be transpiled to ES5 JavaScript.

Babel’s plugin macros and codegen give us a new dimension to manipulate source code at compile time.

In JavaScript, we can have a static value in the source code. For example, a counter that starts at 0. We can also have a dynamic value in the source code. For example, new Date() will return the current time object at runtime.

But can we get a value specifically for compile-time processing (e.g. we want to display a timestamp when this version of code is compiled)?

Yes, we can. preval.macro is perfect for this kind of task.

Babel is a JavaScript transpiler. It enables us to write modern JavaScript that will be transpiled to ES5 JavaScript. In addition, Babel plugins can perform other code transformations during compile time. For our specific example, it can evaluate new Date() at compile time and swap the generated value into a specific location of the source code.

  • babel-plugin-macros: Defines a standard interface for libraries to use compile-time code transformation.
  • babel-plugin-preval: Provides the capability for values generated at compile time to be swapped into the JavaScript file.
  • babel-plugin-codegen: Provides the capability for code generated at compile time to be swapped into the JavaScript file.

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