Jerko Steiner
fb41c2ce69
This is to help guard against types that can be undefined since the
recommended eslint rules recommend against using `!` operator on values
like:
const obj: Obj | undefined = ...
obj!.value
Now we can use:
const obj: Obj | undefined = ...
const obj2: Obj = guard(isDefined, obj)
obj.value
The guard function will throw an error if obj parameter is undefined.
36 lines
695 B
TypeScript
36 lines
695 B
TypeScript
type CheckType<T> = (t: unknown) => t is T
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export function guard<Expected>(
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checkType: CheckType<Expected>,
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t: unknown,
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): Expected {
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if (!checkType(t)) {
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throw new Error(
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`Value ${t} does not satisfy constraint: ${checkType.name}`)
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}
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return t
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}
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export function isUndefined(t: unknown): t is undefined {
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return t === undefined
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}
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export function isNull(t: unknown): t is null {
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return t === null
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}
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export function isDefined<T>(
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t: unknown,
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): t is T {
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return t !== undefined && t !== null
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}
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export function isNumber(t: unknown): t is number {
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return typeof t === 'number'
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}
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export function isString(t: unknown): t is string {
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return typeof t === 'string'
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}
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