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70 lines
2.3 KiB
70 lines
2.3 KiB
# Warning [](https://badge.fury.io/js/warning)
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[](https://greenkeeper.io/)
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A mirror of Facebook's [Warning](https://github.com/facebook/fbjs/blob/master/packages/fbjs/src/__forks__/warning.js)
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## Usage
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```
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npm install warning
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```
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```
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// some script
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var warning = require('warning');
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var ShouldBeTrue = false;
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warning(
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ShouldBeTrue,
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'This thing should be true but you set to false. No soup for you!'
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);
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// 'This thing should be true but you set to false. No soup for you!'
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```
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Similar to Facebook's (FB) invariant but only logs a warning if the condition is not met.
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This can be used to log issues in development environments in critical
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paths. Removing the logging code for production environments will keep the
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same logic and follow the same code paths.
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## FAQ (READ before opening an issue)
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> Why do you use `console.error` instead of `console.warn` ?
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This is a mirror of Facebook's (FB) [warning](https://github.com/facebook/fbjs/blob/master/packages/fbjs/src/__forks__/warning.js) module used within React's source code (and other FB software).
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As such this module will mirror their code as much as possible.
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The descision to use `error` over `warn` was made a long time ago by the FB team and isn't going to change anytime soon.
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The source can be found here: https://github.com/facebook/fbjs/blob/master/packages/fbjs/src/__forks__/warning.js
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The reasoning can be found here and elsewhere: https://github.com/facebook/fbjs/pull/94#issuecomment-168332326
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> Can I add X feature?
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This is a mirror of Facebook's (FB) [warning](https://github.com/facebook/fbjs/blob/master/packages/fbjs/src/__forks__/warning.js) and as such the source and signature will mirror that module.
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If you believe a feature is missing than please open a feature request [there](https://github.com/facebook/fbjs).
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If it is approved and merged in that this module will be updated to reflect that change, otherwise this module will not change.
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## Use in Production
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It is recommended to add [babel-plugin-dev-expression](https://github.com/4Catalyzer/babel-plugin-dev-expression) with this module to remove warning messages in production.
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<small>Don't Forget To Be Awesome</small>
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