90 lines
2.2 KiB
Markdown
90 lines
2.2 KiB
Markdown
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# generate-function
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Module that helps you write generated functions in Node
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```
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npm install generate-function
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```
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[](http://travis-ci.org/mafintosh/generate-function)
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## Disclamer
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Writing code that generates code is hard.
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You should only use this if you really, really, really need this for performance reasons (like schema validators / parsers etc).
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## Usage
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``` js
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const genfun = require('generate-function')
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const { d } = genfun.formats
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function addNumber (val) {
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const gen = genfun()
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gen(`
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function add (n) {')
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return n + ${d(val)}) // supports format strings to insert values
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}
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`)
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return gen.toFunction() // will compile the function
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}
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const add2 = addNumber(2)
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console.log('1 + 2 =', add2(1))
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console.log(add2.toString()) // prints the generated function
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```
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If you need to close over variables in your generated function pass them to `toFunction(scope)`
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``` js
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function multiply (a, b) {
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return a * b
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}
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function addAndMultiplyNumber (val) {
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const gen = genfun()
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gen(`
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function (n) {
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if (typeof n !== 'number') {
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throw new Error('argument should be a number')
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}
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const result = multiply(${d(val)}, n + ${d(val)})
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return result
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}
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`)
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// use gen.toString() if you want to see the generated source
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return gen.toFunction({multiply})
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}
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const addAndMultiply2 = addAndMultiplyNumber(2)
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console.log(addAndMultiply2.toString())
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console.log('(3 + 2) * 2 =', addAndMultiply2(3))
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```
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You can call `gen(src)` as many times as you want to append more source code to the function.
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## Variables
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If you need a unique safe identifier for the scope of the generated function call `str = gen.sym('friendlyName')`.
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These are safe to use for variable names etc.
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## Object properties
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If you need to access an object property use the `str = gen.property('objectName', 'propertyName')`.
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This returns `'objectName.propertyName'` if `propertyName` is safe to use as a variable. Otherwise
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it returns `objectName[propertyNameAsString]`.
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If you only pass `gen.property('propertyName')` it will only return the `propertyName` part safely
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## License
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MIT
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