Added options.from

index.js

@@ -27,7 +27,7 @@ module.exports = function(val, options) {
   options = options || {};
   var type = typeof val;
   if (type === 'string' && val.length > 0) {
-    return parse(val);
+    return options.from ? calcFrom(val, options.from) : parse(val);
   } else if (type === 'number' && isNaN(val) === false) {
     return options.long ? fmtLong(val) : fmtShort(val);
   }
@@ -157,3 +157,20 @@ function plural(ms, n, name) {
   }
   return Math.ceil(ms / n) + ' ' + name + 's';
 }
+
+/**
+ * Calculate the milliseconds for given date
+ * @param  {String} str
+ * @param  {Date} date
+ * @return {Number}
+ * @api private
+ */
+function calcFrom(str, date) {
+  if (new Date(date).toString() === 'Invalid Date' || date === true)
+    throw new Error(
+      'option.from is not a valid Date. options.from=' + JSON.stringify(date)
+    );
+  var ms = parse(str);
+
+  return new Date(date).getTime() + ms;
+}

tests.js

@@ -229,3 +229,23 @@ describe('ms(invalid inputs)', function() {
     }).to.throwError();
   });
 });
+
+describe('ms(string, { from: Number })', function() {
+  it('should throw an error when options.from is true', function() {
+    expect(function() {
+      ms('1h', { from: true });
+    }).to.throwError();
+  });
+
+  it('should ignore options.from when it is not Number', function() {
+    expect(ms('1h', { from: '' })).to.be(3600000);
+    expect(ms('1h', { from: NaN })).to.be(3600000);
+  });
+
+  it('should add time to unix epoch time', function() {
+    expect(ms('1ms', { from: new Date(0) })).to.be(1);
+    expect(ms('1s', { from: new Date(0) })).to.be(1000);
+    expect(ms('1m', { from: new Date(0) })).to.be(60000);
+    expect(ms('1h', { from: new Date(0) })).to.be(3600000);
+  });
+});