add incrementNumeric to Lib make it reusable and testable

force magic number to be positive to avoid getting -0

Author: archmoj

src/lib/increment_numeric.js

@@ -0,0 +1,37 @@
+/**
+* Copyright 2012-2019, Plotly, Inc.
+* All rights reserved.
+*
+* This source code is licensed under the MIT license found in the
+* LICENSE file in the root directory of this source tree.
+*/
+
+
+'use strict';
+
+module.exports = function incrementNumeric(x, delta) {
+    if(!delta) return x;
+
+    // Note 1:
+    // 0.3 != 0.1 + 0.2 == 0.30000000000000004
+    // but 0.3 == (10 * 0.1 + 10 * 0.2) / 10
+    // Attempt to use integer steps to increment
+    var magic = 1 / Math.abs(delta);
+    var newX = (
+        magic * x +
+        magic * delta
+    ) / magic;
+
+    // Note 2:
+    // now we may also consider rounding to cover few more edge cases
+    // e.g. 0.3 * 3 = 0.8999999999999999
+    var lenDt = ('' + delta).length;
+    var lenX0 = ('' + x).length;
+    var lenX1 = ('' + newX).length;
+
+    if(lenX1 > lenX0 + lenDt) { // likely a rounding error!
+        newX = +parseFloat(newX).toPrecision(12);
+    }
+
+    return newX;
+};

src/lib/index.js

@@ -149,6 +149,8 @@ lib.clearResponsive = require('./clear_responsive');
 
 lib.makeTraceGroups = require('./make_trace_groups');
 
+lib.incrementNumeric = require('./increment_numeric');
+
 lib._ = require('./localize');
 
 lib.notifier = require('./notifier');

src/plots/cartesian/axes.js

@@ -847,27 +847,7 @@ axes.tickIncrement = function(x, dtick, axrev, calendar) {
     var axSign = axrev ? -1 : 1;
 
     // includes linear, all dates smaller than month, and pure 10^n in log
-    if(isNumeric(dtick)) {
-        // Note 1:
-        // 0.3 != 0.1 + 0.2 but 0.3 == ((10 * 0.1) + (10 * 0.2)) / 10
-        // Attempt to use integer steps to increment
-        var magic = 1 / dtick;
-        var newX = (
-            magic * x +
-            magic * axSign * dtick
-        ) / magic;
-
-        // Note 2: now we may also consider rounding to cover few more edge cases
-        var lenDt = ('' + dtick).length;
-        var lenX0 = ('' + x).length;
-        var lenX1 = ('' + newX).length;
-
-        if(lenX1 > lenX0 + lenDt) { // this is likey a rounding error!
-            newX = +parseFloat(newX).toPrecision(12);
-        }
-
-        return newX;
-    }
+    if(isNumeric(dtick)) return Lib.incrementNumeric(x, axSign * dtick);
 
     // everything else is a string, one character plus a number
     var tType = dtick.charAt(0);