constantinople

Determine whether a JavaScript expression evaluates to a constant (using Babylon). 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, [options]])

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.

Options are directly passed-through to Babylon.

toConstant(src, [constants, [options]])

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.