47 lines
2.0 KiB
Markdown
47 lines
2.0 KiB
Markdown
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# constantinople
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Determine whether a JavaScript expression evaluates to a constant (using Babylon). Here it is assumed to be safe to underestimate how constant something is.
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[](https://travis-ci.org/pugjs/constantinople)
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[](https://david-dm.org/pugjs/constantinople)
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[](https://www.npmjs.org/package/constantinople)
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## Installation
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npm install constantinople
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## Usage
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```js
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var isConstant = require('constantinople');
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if (isConstant('"foo" + 5')) {
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console.dir(isConstant.toConstant('"foo" + 5'));
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}
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if (isConstant('Math.floor(10.5)', {Math: Math})) {
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console.dir(isConstant.toConstant('Math.floor(10.5)', {Math: Math}));
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}
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```
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## API
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### isConstant(src, [constants, [options]])
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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.
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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.
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Options are directly passed-through to [Babylon](https://github.com/babel/babylon#options).
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### toConstant(src, [constants, [options]])
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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.
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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.
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Options are directly passed-through to [Babylon](https://github.com/babel/babylon#options).
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## License
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MIT
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