Compile time `with` for strict mode JavaScript
Compile time with for strict mode JavaScript
$ npm install with
``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));'
`
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 canerror.component
retrieve location information. 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.
MIT