constantinople

What is constantinople?

The 'constantinople' npm package is primarily used to determine if a JavaScript expression is a constant at compile time. This can be particularly useful in template engines, build tools, and other environments where compile-time evaluation can optimize runtime performance by reducing the need for unnecessary computations.

What are constantinople's main functionalities?

Compile-time constant evaluation

This feature allows developers to check if an expression is constant at compile time. The provided code checks if '2 + 2' is a constant expression.

const constantinople = require('constantinople');
if (constantinople.isConstant('2 + 2')) {
  console.log('This is a constant expression.');
}

Other packages similar to constantinople

jstransformer

Like constantinople, jstransformer is used in template engines to transform inputs using a standardized interface. While constantinople focuses on compile-time constant checks, jstransformer provides a broader range of transformations but does not specifically optimize for compile-time constants.

uglify-js

uglify-js is a JavaScript parser, minifier, compressor, and beautifier toolkit. It shares some functionality with constantinople in terms of evaluating expressions during the build process to optimize scripts. However, uglify-js is more comprehensive in scope, focusing on overall code reduction and performance improvements.

README

constantinople

Determine whether a JavaScript expression evaluates to a constant (using UglifyJS). Here it is assumed to be safe to underestimate how constant something is.

Installation

npm install constantinople

Usage

var isConstant = require('constantinople')

if (isConstant('"foo" + 5')) {
  console.dir(isConstant.toConstant('"foo" + 5'))
}
if (isConstant('Math.floor(10.5)', {Math: Math})) {
  console.dir(isConstant.toConstant('Math.floor(10.5)', {Math: Math}))
}

API

isConstant(src, [constants])

Returns true if src evaluates to a constant, false otherwise. It will also return false if there is a syntax error, which makes it safe to use on potentially ES6 code.

Constants is an object mapping strings to values, where those values should be treated as constants. Note that this makes it a pretty bad idea to have Math in there if the user might make use of Math.random and a pretty bad idea to have Date in there.

toConstant(src, [constants])

Returns the value resulting from evaluating src. This method throws an error if the expression is not constant. e.g. toConstant("Math.random()") would throw an error.

Constants is an object mapping strings to values, where those values should be treated as constants. Note that this makes it a pretty bad idea to have Math in there if the user might make use of Math.random and a pretty bad idea to have Date in there.

License

MIT