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# with
Compile time `with` for strict mode JavaScript
[![Build Status](https://img.shields.io/github/workflow/status/pugjs/with/Publish%20Canary/master?style=for-the-badge)](https://github.com/pugjs/with/actions?query=workflow%3A%22Publish+Canary%22)
[![Rolling Versions](https://img.shields.io/badge/Rolling%20Versions-Enabled-brightgreen?style=for-the-badge)](https://rollingversions.com/pugjs/with)
[![NPM version](https://img.shields.io/npm/v/with?style=for-the-badge)](https://www.npmjs.com/package/with)
## Installation
$ npm install with
## Usage
```js
var addWith = require('with');
addWith('obj', 'console.log(a)');
// => ';(function (console, a) {
// console.log(a)
// }("console" in obj ? obj.console :
// typeof console!=="undefined" ? console : undefined,
// "a" in obj ? obj.a :
// typeof a !== "undefined" ? a : undefined));'
addWith('obj', 'console.log(a)', ['console']);
// => ';(function (console, a) {
// console.log(a)
// }("a" in obj ? obj.a :
// typeof a !== "undefined" ? a : undefined));'
```
## API
### addWith(obj, src[, exclude])
The idea is that this is roughly equivallent to:
```js
with (obj) {
src;
}
```
There are a few differences though. For starters, assignments to variables will always remain contained within the with block.
e.g.
```js
var foo = 'foo';
with ({}) {
foo = 'bar';
}
assert(foo === 'bar'); // => This fails for compile time with but passes for native with
var obj = {foo: 'foo'};
with ({}) {
foo = 'bar';
}
assert(obj.foo === 'bar'); // => This fails for compile time with but passes for native with
```
It also makes everything be declared, so you can always do:
```js
if (foo === undefined)
```
instead of
```js
if (typeof foo === 'undefined')
```
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.
It is also safe to use in strict mode (unlike `with`) and it minifies properly (`with` disables virtually all minification).
#### Parsing Errors
with internally uses babylon to parse code passed to `addWith`. If babylon throws an error, probably due to a syntax error, `addWith` returns an error wrapping the babylon error, so you can
retrieve location information. `error.component` is `"src"` if the error is in the body or `"obj"` if it's in the object part of the with expression. `error.babylonError` is
the error thrown from babylon.
## License
MIT