Make new BigDecimal produce better errors

src/BigDecimal.test.ts

@@ -32,6 +32,28 @@ function testUnnecessary(
   }
 }
 
+test("BigDecimal parsing", (t) => {
+  const passes = new BigDecimal("1.1")
+  t.is(passes.toString(), "1.1")
+  t.is(passes.scale(), 1)
+  t.is(passes.unscaledValue(), 11n)
+
+  let e = t.throws(() => new BigDecimal("1.1.1"))
+  t.snapshot(e, "too many decimal places")
+  e = t.throws(() => new BigDecimal("1.1e1"))
+  t.snapshot(e, "weird exponential notation")
+  e = t.throws(() => new BigDecimal("1.1e10"))
+  t.snapshot(e, "normal exponential notation")
+  e = t.throws(() => new BigDecimal("1.1e"))
+  t.snapshot(e, "other weird exponential notation")
+  e = t.throws(() => new BigDecimal("1.1e1.1"))
+  t.snapshot(e, "super weird exponential notation")
+  e = t.throws(() => new BigDecimal("abcd"))
+  t.snapshot(e, "not a number")
+  e = t.throws(() => new BigDecimal("zxy"))
+  t.snapshot(e, "another not a number")
+})
+
 test("BigDecimal rounding", (t) => {
   testRounding(t, "5.5", "6", {
     precision: 0,

src/BigDecimal.test.ts.md

@@ -4,6 +4,50 @@ The actual snapshot is saved in `BigDecimal.test.ts.snap`.
 
 Generated by [AVA](https://avajs.dev).
 
+## BigDecimal parsing
+
+> too many decimal places
+
+    Error {
+      message: 'BigDecimal: multiple decimal points found',
+    }
+
+> weird exponential notation
+
+    Error {
+      message: 'BigDecimal: exponential notation is not supported',
+    }
+
+> normal exponential notation
+
+    Error {
+      message: 'BigDecimal: exponential notation is not supported',
+    }
+
+> other weird exponential notation
+
+    Error {
+      message: 'BigDecimal: exponential notation is not supported',
+    }
+
+> super weird exponential notation
+
+    Error {
+      message: 'BigDecimal: exponential notation is not supported',
+    }
+
+> not a number
+
+    Error {
+      message: 'BigDecimal: not a number',
+    }
+
+> another not a number
+
+    Error {
+      message: 'BigDecimal: not a number',
+    }
+
 ## BigDecimal.compareTo
 
 > Snapshot 1

src/BigDecimal.ts

@@ -93,10 +93,21 @@ export class BigDecimal {
     }
 
     // split into integer and decimal parts
-    const [integer, decimal] = str.split(".")
+    const [integer, decimal, ...rest] = str.split(".")
+    if (rest.length > 0) {
+      error("BigDecimal: multiple decimal points found")
+    }
 
     // The unscaled value is the integer part followed by the decimal part
-    this.#value = BigInt(`${integer}${decimal ?? ""}`)
+    try {
+      this.#value = BigInt(`${integer}${decimal ?? ""}`)
+    } catch (e) {
+      if (e instanceof SyntaxError) {
+        error("BigDecimal: not a number")
+      }
+
+      throw e
+    }
     // The initial scale is either given (needed for certain math operations) or the length of the decimal part
     this.#scale = scale ?? decimal?.length ?? 0