1+ import isNumber from 'lodash/isNumber' ;
2+
3+ /**
4+ * The base for the whole library. Run predicate on the value.
5+ * If predicate returns true, returns the value as is. Otherwise, throws
6+ * with the given message.
7+ * If you just want a condition, not a type assertion, use `beTrue`
8+ * @param val {any} The value itself.
9+ * @param predicate {(a: any) => a is T}. As you can see, the predicate should
10+ * assert a type
11+ * @param errorMessage {string}
12+ */
13+ export function be < T > (
14+ val : any ,
15+ predicate : ( a : any ) => a is T ,
16+ errorMessage : string ,
17+ ) : T {
18+ if ( predicate ( val ) ) return val ;
19+
20+ throw new TypeError ( errorMessage ) ;
21+ }
22+
23+ /**
24+ * Checks for a condition that is not a type assertion. Ergo cannot
25+ * narrow done the value type and returns the same type it gets.
26+ * If you want to assert and narrow down types, use `be`.
27+ * @param val {T} The value itself.
28+ * @param predicate: {(a: T) => boolean}.
29+ * @param errorMessage {string}
30+ */
31+ export function beTrue < T > (
32+ val : T ,
33+ predicate : ( a : T ) => boolean ,
34+ errorMessage : string ,
35+ ) : T {
36+ if ( predicate ( val ) ) return val ;
37+
38+ throw new Error ( errorMessage ) ;
39+ }
40+
41+ type CatchOptions = {
42+ logger ?: ( e : Error ) => void ;
43+ }
44+
45+ const noop = ( ) => { }
46+
47+ /**
48+ * Runs a decoding function, and if all the validations succeed, returns
49+ * the value. If something fails, falls back to another value (and optionally
50+ * logs the error).
51+ * @param make {() => T} The function that generates the expected type (and throws on invalid data)
52+ * @param fallback {U} The fallback value (probably different from T)
53+ * @param options {CatchOptions}
54+ */
55+ export function orBe < T , U > (
56+ make : ( ) => T ,
57+ fallback : U ,
58+ { logger = noop } : CatchOptions = { }
59+ ) : T | U {
60+ try {
61+ return make ( )
62+ } catch ( e ) {
63+ /*
64+ If we ever add a custom error, we should replace all the
65+ `new TypeError` invocations. But frankly, why not catch all
66+ exceptions indiscriminately, even those not foreseen
67+ by a programmer.
68+ */
69+ logger ( e )
70+ return fallback
71+ }
72+ }
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