avoid dividing by zero & handle single value

asciichart.js

@@ -17,7 +17,7 @@
         let offset  = (typeof cfg.offset  !== 'undefined') ? cfg.offset  : 3
         let padding = (typeof cfg.padding !== 'undefined') ? cfg.padding : '           '
         let height  = (typeof cfg.height  !== 'undefined') ? cfg.height  : range
-        let ratio   = height / range
+        let ratio   = range !== 0 ? height / range : 1;
         let min2    = Math.round (min * ratio)
         let max2    = Math.round (max * ratio)
         let rows    = Math.abs (max2 - min2)
@@ -33,9 +33,8 @@
                 result[i][j] = ' '
             }
         }
-
         for (let y = min2; y <= max2; ++y) { // axis + labels
-            let label = format (max - (y - min2) * range / rows, y - min2)
+            let label = format (rows > 0 ? max - (y - min2) * range / rows : y, y - min2)
             result[y - min2][Math.max (offset - label.length, 0)] = label
             result[y - min2][offset - 1] = (y == 0) ? '┼' : '┤'
         }
@@ -62,4 +61,4 @@
         return result.map (function (x) { return x.join ('') }).join ('\n')
     }
 
-}) (typeof exports === 'undefined' ? /* istanbul ignore next */ this['asciichart'] = {} : exports);
+}) (typeof exports === 'undefined' ? /* istanbul ignore next */ this['asciichart'] = {} : exports);

test.js

@@ -36,4 +36,12 @@ var s2 = new Array (width)
 s2[0] = Math.round (Math.random () * 15)
 for (i = 1; i < s2.length; i++)
     s2[i] = s2[i - 1] + Math.round (Math.random () * (Math.random () > 0.5 ? 2 : -2))
-console.log (asciichart.plot (s2) + "\n")
+console.log (asciichart.plot (s2) + "\n")
+
+console.log (line)
+console.log ("single value\n")
+
+var s3 = new Array (width)
+for (i = 0; i < width; i++)
+    s3[i] = 1.0
+console.log (asciichart.plot (s3) + "\n")