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A tiny invariant
alternative.
invariant
?An invariant
function takes a value, and if the value is falsy then the invariant
function will throw. If the value is truthy, then the function will not throw.
import invariant from 'tiny-invariant';
invariant(truthyValue, 'This should not throw!');
invariant(falsyValue, 'This will throw!');
// Error('Invariant violation: This will throw!');
tiny-invariant
?The library: invariant
supports passing in arguments to the invariant
function in a sprintf style (condition, format, a, b, c, d, e, f)
. It has internal logic to execute the sprintf substitutions. The sprintf logic is not removed in production builds. tiny-invariant
has dropped all of the sprintf logic. tiny-invariant
allows you to pass a single string message. With template literals there is really no need for a custom message formatter to be built into the library. If you need a multi part message you can just do this: invariant(condition, 'Hello, ${name} - how are you today?')
tiny-invariant
is useful for correctly narrowing types for flow
and typescript
const value: Person | null = { name: 'Alex' }; // type of value == 'Person | null'
invariant(value, 'Expected value to be a person');
// type of value has been narrowed to 'Person'
(condition: any, message?: string) => void
condition
is required and can be anythingmessage
is an optional string# yarn
yarn add tiny-invariant
# npm
npm add tiny-invariant --save
message
for kb savings!Big idea: you will want your compiler to convert this code:
invariant(condition, 'My cool message that takes up a lot of kbs');
Into this:
if (!condition) {
if ('production' !== process.env.NODE_ENV) {
invariant(false, 'My cool message that takes up a lot of kbs');
} else {
invariant(false);
}
}
babel-plugin-dev-expression
tsdx
(or you can run babel-plugin-dev-expression
after TypeScript compiling)Your bundler can then drop the code in the "production" !== process.env.NODE_ENV
block for your production builds to end up with this:
if (!condition) {
invariant(false);
}
NODE_ENV
to production
and then rollup
will treeshake out the unused codees
(EcmaScript module) build (because you know you want to deduplicate this super heavy library)cjs
(CommonJS) buildumd
(Universal module definition) build in case you needed itWe expect process.env.NODE_ENV
to be available at module compilation. We cache this value
🤘