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81 lines
2.0 KiB
Markdown
81 lines
2.0 KiB
Markdown
5 years ago
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# with
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Compile time `with` for strict mode JavaScript
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[](http://travis-ci.org/ForbesLindesay/with)
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[](https://gemnasium.com/ForbesLindesay/with)
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[](http://badge.fury.io/js/with)
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## Installation
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$ npm install with
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## Usage
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```js
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var addWith = require('with')
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addWith('obj', 'console.log(a)')
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// => ';(function (console, a) {
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// console.log(a)
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// }("console" in obj ? obj.console :
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// typeof console!=="undefined" ? console : undefined,
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// "a" in obj ? obj.a :
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// typeof a !== "undefined" ? a : undefined));'
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addWith('obj', 'console.log(a)', ['console'])
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// => ';(function (console, a) {
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// console.log(a)
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// }("a" in obj ? obj.a :
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// typeof a !== "undefined" ? a : undefined));'
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```
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## API
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### addWith(obj, src[, exclude])
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The idea is that this is roughly equivallent to:
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```js
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with (obj) {
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src
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}
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```
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There are a few differences though. For starters, assignments to variables will always remain contained within the with block.
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e.g.
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```js
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var foo = 'foo'
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with ({}) {
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foo = 'bar'
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}
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assert(foo === 'bar')// => This fails for compile time with but passes for native with
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var obj = {foo: 'foo'}
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with ({}) {
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foo = 'bar'
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}
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assert(obj.foo === 'bar')// => This fails for compile time with but passes for native with
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```
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It also makes everything be declared, so you can always do:
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```js
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if (foo === undefined)
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```
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instead of
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```js
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if (typeof foo === 'undefined')
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```
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This is not the case if foo is in `exclude`. If a variable is excluded, we ignore it entirely. This is useful if you know a variable will be global as it can lead to efficiency improvements.
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It is also safe to use in strict mode (unlike `with`) and it minifies properly (`with` disables virtually all minification).
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## License
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MIT
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