extra-lazy
v2.0.2
Published
Yet another lazy evaluation library.
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10,072
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extra-lazy
Yet another lazy evaluation library.
Install
npm install --save extra-lazy
# or
yarn add extra-lazy
Usage
import { lazy } from 'extra-lazy'
const getValue = lazy(() => {
// ...
return value
})
const value = getValue()
API
lazy
function lazy<T>(getter: () => T): () => T
Create a value lazily.
which implicitly has memoization, because the evaluation will only be performed once.
weakLazy
function weakLazy<T extends object>(getter: () => T): () => T
lazyFunction
function lazyFunction<Result, Args extends any[]>(
getter: () => (...args: Args) => Result
): (...args: Args) => Result
Create a function lazily.
lazyAsyncFunction
function lazyAsyncFunction<Result, Args extends any[]>(
getter: () => PromiseLike<(...args: Args) => Result>
): (...args: Args) => Promise<Result>
Create a async function lazily.
lazyStatic
function lazyStatic<T>(
getter: () => T
, deps?: unknown[] = []
): T
/**
* @param fn
* The function must satisfy the following conditions, it's like React hooks very much:
* - The function should not be an async function,
* it is impossible to ensure that `lazyStatic` works correctly in asynchronous flows.
* - `lazyStatic` calls should not be in loops or branches.
*/
function withLazyStatic<Result, Args extends any[]>(
fn: (...args: Args) => Result
): (...args: Args) => Result
Example:
const fn = withLazyStatic((text: string) => lazyStatic(() => text))
fn('hello') // 'hello'
fn('world') // 'hello'
Best practices
Loop
// bad
withLazyStatic(() => {
while (condition) {
const value = lazyStatic(() => {
// ...
})
// ...
}
})
// good
withLazyStatic(() => {
const value = lazyStatic(() => {
// ...
})
while (condition) {
// ...
}
})
Branch
// bad
withLazyStatic(() => {
if (condition) {
const value = lazyStatic(() => {
// ...
})
// ...
} else {
// ...
}
})
// good
withLazyStatic(() => {
const value = lazyStatic(() => {
// ...
})
if (condition) {
// ...
} else {
// ...
}
})
Assertion/Validation
// bad
withLazyStatic((form: IForm) => {
if (validate(form)) {
const value = lazyStatic(() => {
// ...
})
// ...
} else {
const value = lazyStatic(() => {
// ...
})
return null // or throw an error
}
})
// okay
withLazyStatic((form: IForm) => {
if (validate(form)) {
const value = lazyStatic(() => {
// ...
})
// ...
} else {
return null // or throw an error
}
})
// good, `lazyStatic` can always be called after guards
withLazyStatic((form: IForm) => {
if (!validate(form)) return null // or throw an error
const value = lazyStatic(() => {
// ...
})
// ...
})