Handle empty tax table

diff --git a/tax.js b/tax.js
index 0d94200ce97849d3e97d73e5fce84e44dd98f26d..d26db5fa15f0b8cf0cdd006fd4b19cc4f6e37076 100644 (file)
--- a/tax.js
+++ b/tax.js
@@ -49,6 +49,8 @@ function merge_tax_tables(t1, t2) {
 }
 
 function invert(table) {
+  if (table.length == 0) return x => x;
+
   // Here we solve
   //   net = m * gross + b
   // for gross:

diff --git a/tax.test.js b/tax.test.js
index 19597fbc2ae629fc71f399e9b67c2d884065db17..48f2e0dda7437785ccf317e5094575b6b42b1d95 100644 (file)
--- a/tax.test.js
+++ b/tax.test.js
@@ -47,6 +47,7 @@ test("merge tax tables", () => {
 });
 
 test("invert", () => {
+  assert.strictEqual(invert([                  ])(10), 10);
   assert.strictEqual(invert([[ 0, Infinity, .1]])( 9), 10);
   assert.strictEqual(invert([[10, Infinity, .1]])(19), 20);
   assert.strictEqual(invert([[0, 100, .1], [100, Infinity, .2]])(170), 200);