From d371712afa5d3281df9aa98099e2148b776dfb58 Mon Sep 17 00:00:00 2001
From: Amio <amio.cn@gmail.com>
Date: Wed, 18 Jul 2018 13:59:40 +0800
Subject: [PATCH] Improve error handling

---
 lib/calc-text-width.js       | 24 +++++++++++++-----------
 test/calc-text-width.spec.js |  5 +++++
 2 files changed, 18 insertions(+), 11 deletions(-)

diff --git a/lib/calc-text-width.js b/lib/calc-text-width.js
index f66b458..79ff612 100644
--- a/lib/calc-text-width.js
+++ b/lib/calc-text-width.js
@@ -4,21 +4,23 @@ function calcWidth (charWidthTable) {
   const SCALE = 10
   const widthTable = charWidthTable.map(w => Math.round(w * SCALE))
   return function (text) {
-    if (typeof text !== 'string') {
-      return 0
-    } else {
-      let total = 0
-      let i = text.length
-      let charCode = 0
-      while (i--) {
-        charCode = text[i].charCodeAt()
-        total += widthTable[charCode < 127 ? charCode : 64] // "@" for overflows
-      }
-      return total / SCALE
+    typeAssert(typeof text === 'string', 'Input must be string')
+
+    let total = 0
+    let i = text.length
+    let charCode = 0
+    while (i--) {
+      charCode = text[i].charCodeAt()
+      total += widthTable[charCode < 127 ? charCode : 64] // "@" for overflows
     }
+    return total / SCALE
   }
 }
 
+const typeAssert = (assertion, message) => {
+  if (!assertion) throw new TypeError(message)
+}
+
 module.exports = {
   Verdana11: calcWidth(widthsVerdana11)
 }
diff --git a/test/calc-text-width.spec.js b/test/calc-text-width.spec.js
index 768ee59..8399242 100644
--- a/test/calc-text-width.spec.js
+++ b/test/calc-text-width.spec.js
@@ -7,3 +7,8 @@ tap.test('calc width for "npm"', t => {
   t.is(calcWidth('npm'), 24.9, 'result is correct value')
   t.end()
 })
+
+tap.test('exception handling', t => {
+  t.throws(() => calcWidth(0), TypeError, 'throw if feed with non-string input')
+  t.end()
+})