diff --git a/lib/constants.js b/lib/constants.js
index 3cba467b5..bf248cb83 100644
--- a/lib/constants.js
+++ b/lib/constants.js
@@ -77,4 +77,4 @@ function setLazyConstant (math, name, resolver) {
 
 exports.factory = factory;
 exports.lazy = false;  // no lazy loading of constants, the constants themselves are lazy when needed
-exports.math = true;   // request access to the math namespace
\ No newline at end of file
+exports.math = true;   // request access to the math namespace
diff --git a/lib/core/core.js b/lib/core/core.js
index acc732366..eea7b27ca 100644
--- a/lib/core/core.js
+++ b/lib/core/core.js
@@ -1,3 +1,4 @@
+'use strict';
 var isFactory = require('./../utils/object').isFactory;
 var typedFactory = require('./typed');
 var emitter = require('./../utils/emitter');
diff --git a/lib/core/typed.js b/lib/core/typed.js
index b3819750a..73a2483b0 100644
--- a/lib/core/typed.js
+++ b/lib/core/typed.js
@@ -1,3 +1,4 @@
+'use strict';
 var typedFunction = require('typed-function');
 var digits = require('./../utils/number').digits;
 var isBigNumber = require('./../utils/bignumber/isBigNumber');
diff --git a/lib/expression/function/eval.js b/lib/expression/function/eval.js
index 3a74fbdca..09969bf0e 100644
--- a/lib/expression/function/eval.js
+++ b/lib/expression/function/eval.js
@@ -63,4 +63,4 @@ function factory (type, config, load, typed) {
 }
 
 exports.name = 'eval';
-exports.factory = factory;
\ No newline at end of file
+exports.factory = factory;
diff --git a/lib/expression/function/index.js b/lib/expression/function/index.js
index dc7082a4c..1af02d167 100644
--- a/lib/expression/function/index.js
+++ b/lib/expression/function/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   require('./compile'),
   require('./eval'),
diff --git a/lib/expression/index.js b/lib/expression/index.js
index 6f8200160..704a175fe 100644
--- a/lib/expression/index.js
+++ b/lib/expression/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   // Note that the docs folder is called "embeddedDocs" and not "docs" to prevent issues
   // with yarn autoclean. See https://github.com/josdejong/mathjs/issues/969
diff --git a/lib/expression/node/index.js b/lib/expression/node/index.js
index 8c49ae109..b9fff2366 100644
--- a/lib/expression/node/index.js
+++ b/lib/expression/node/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   require('./AccessorNode'),
   require('./ArrayNode'),
diff --git a/lib/expression/transform/error.transform.js b/lib/expression/transform/error.transform.js
index 5bf4adb32..6b791cdd6 100644
--- a/lib/expression/transform/error.transform.js
+++ b/lib/expression/transform/error.transform.js
@@ -1,3 +1,4 @@
+'use strict';
 var IndexError = require('../../error/IndexError');
 
 /**
diff --git a/lib/expression/transform/index.js b/lib/expression/transform/index.js
index dc82da5bb..c9c77b08c 100644
--- a/lib/expression/transform/index.js
+++ b/lib/expression/transform/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   require('./concat.transform'),
   require('./filter.transform'),
diff --git a/lib/expression/transform/utils/compileInlineExpression.js b/lib/expression/transform/utils/compileInlineExpression.js
index 0467d393b..2e2cf5938 100644
--- a/lib/expression/transform/utils/compileInlineExpression.js
+++ b/lib/expression/transform/utils/compileInlineExpression.js
@@ -1,3 +1,4 @@
+'use strict';
 function factory (type, config, load, typed) {
   /**
    * Compile an inline expression like "x > 0"
diff --git a/lib/function/algebra/index.js b/lib/function/algebra/index.js
index 8801e7df9..592b1addd 100644
--- a/lib/function/algebra/index.js
+++ b/lib/function/algebra/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   require('./derivative'),
 
diff --git a/lib/function/algebra/rationalize.js b/lib/function/algebra/rationalize.js
index 2d989c5ec..216aa9516 100644
--- a/lib/function/algebra/rationalize.js
+++ b/lib/function/algebra/rationalize.js
@@ -604,4 +604,4 @@ function factory (type, config, load, typed) {
 } // end of factory
 
 exports.name = 'rationalize';
-exports.factory = factory;
\ No newline at end of file
+exports.factory = factory;
diff --git a/lib/function/algebra/simplify/util.js b/lib/function/algebra/simplify/util.js
index b61378850..92b36c392 100644
--- a/lib/function/algebra/simplify/util.js
+++ b/lib/function/algebra/simplify/util.js
@@ -155,4 +155,4 @@ function factory(type, config, load, typed, math) {
 }
 
 exports.factory = factory;
-exports.math = true;
\ No newline at end of file
+exports.math = true;
diff --git a/lib/function/algebra/solver/utils/solveValidation.js b/lib/function/algebra/solver/utils/solveValidation.js
index 1f9050830..5dd22089f 100644
--- a/lib/function/algebra/solver/utils/solveValidation.js
+++ b/lib/function/algebra/solver/utils/solveValidation.js
@@ -159,4 +159,4 @@ function factory (type) {
   return solveValidation;
 }
 
-exports.factory = factory;
\ No newline at end of file
+exports.factory = factory;
diff --git a/lib/function/arithmetic/index.js b/lib/function/arithmetic/index.js
index cca4cd9d5..2f6c5b969 100644
--- a/lib/function/arithmetic/index.js
+++ b/lib/function/arithmetic/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   require('./abs'),
   require('./add'),
diff --git a/lib/function/bitwise/index.js b/lib/function/bitwise/index.js
index 232ea7a91..579fa2081 100644
--- a/lib/function/bitwise/index.js
+++ b/lib/function/bitwise/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   require('./bitAnd'),
   require('./bitNot'),
diff --git a/lib/function/combinatorics/index.js b/lib/function/combinatorics/index.js
index 245a5b97c..9555ec7fb 100644
--- a/lib/function/combinatorics/index.js
+++ b/lib/function/combinatorics/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   require('./bellNumbers'),
   require('./composition'),
diff --git a/lib/function/complex/index.js b/lib/function/complex/index.js
index e51f8ead2..9b2ce2b81 100644
--- a/lib/function/complex/index.js
+++ b/lib/function/complex/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   require('./arg'),
   require('./conj'),
diff --git a/lib/function/geometry/index.js b/lib/function/geometry/index.js
index 267024ba6..2c1d75ce9 100644
--- a/lib/function/geometry/index.js
+++ b/lib/function/geometry/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   require('./intersect'),
   require('./distance')
diff --git a/lib/function/index.js b/lib/function/index.js
index 0a9a59819..7d386bd99 100644
--- a/lib/function/index.js
+++ b/lib/function/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   require('./algebra'),
   require('./arithmetic'),
diff --git a/lib/function/logical/index.js b/lib/function/logical/index.js
index ddd746cf2..4ec020184 100644
--- a/lib/function/logical/index.js
+++ b/lib/function/logical/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   require('./and'),
   require('./not'),
diff --git a/lib/function/matrix/index.js b/lib/function/matrix/index.js
index 0a30c8a93..10a004fcd 100644
--- a/lib/function/matrix/index.js
+++ b/lib/function/matrix/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   require('./concat'),
   require('./cross'),
diff --git a/lib/function/probability/index.js b/lib/function/probability/index.js
index 91783721e..365571cb1 100644
--- a/lib/function/probability/index.js
+++ b/lib/function/probability/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   //require('./distribution'), // TODO: rethink math.distribution
   require('./combinations'),
diff --git a/lib/function/relational/index.js b/lib/function/relational/index.js
index 56b1a8d42..3272bf501 100644
--- a/lib/function/relational/index.js
+++ b/lib/function/relational/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   require('./compare'),
   require('./compareNatural'),
diff --git a/lib/function/set/index.js b/lib/function/set/index.js
index b4d0b79ec..6bf5bb049 100644
--- a/lib/function/set/index.js
+++ b/lib/function/set/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   require('./setCartesian'),
   require('./setDifference'),
diff --git a/lib/function/special/index.js b/lib/function/special/index.js
index 1fd1b35e2..63b4d620d 100644
--- a/lib/function/special/index.js
+++ b/lib/function/special/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   require('./erf')
 ];
diff --git a/lib/function/statistics/index.js b/lib/function/statistics/index.js
index 1e8197647..9ac177ea0 100644
--- a/lib/function/statistics/index.js
+++ b/lib/function/statistics/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   require('./mad'),
   require('./max'),
diff --git a/lib/function/statistics/mode.js b/lib/function/statistics/mode.js
index 267b5541f..e308b09cc 100644
--- a/lib/function/statistics/mode.js
+++ b/lib/function/statistics/mode.js
@@ -74,4 +74,4 @@ function factory (type, config, load, typed) {
 }
 
 exports.name = 'mode';
-exports.factory = factory;
\ No newline at end of file
+exports.factory = factory;
diff --git a/lib/function/statistics/utils/improveErrorMessage.js b/lib/function/statistics/utils/improveErrorMessage.js
index 68b961ba0..c180ec952 100644
--- a/lib/function/statistics/utils/improveErrorMessage.js
+++ b/lib/function/statistics/utils/improveErrorMessage.js
@@ -1,3 +1,4 @@
+'use strict';
 
 
 function factory (type, config, load, typed) {
diff --git a/lib/function/string/index.js b/lib/function/string/index.js
index 0c2e76550..8e9654d15 100644
--- a/lib/function/string/index.js
+++ b/lib/function/string/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   require('./format'),
   require('./print')
diff --git a/lib/function/trigonometry/index.js b/lib/function/trigonometry/index.js
index ea97ea22c..61b9f4161 100644
--- a/lib/function/trigonometry/index.js
+++ b/lib/function/trigonometry/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   require('./acos'),
   require('./acosh'),
diff --git a/lib/function/unit/index.js b/lib/function/unit/index.js
index 284e90395..673dcef8d 100644
--- a/lib/function/unit/index.js
+++ b/lib/function/unit/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   require('./to')
-];
\ No newline at end of file
+];
diff --git a/lib/function/utils/index.js b/lib/function/utils/index.js
index 11a054bec..8cbf689bc 100644
--- a/lib/function/utils/index.js
+++ b/lib/function/utils/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   require('./clone'),
   require('./isInteger'),
diff --git a/lib/header.js b/lib/header.js
index 2715aacf1..07f008be3 100644
--- a/lib/header.js
+++ b/lib/header.js
@@ -1,3 +1,4 @@
+'use strict';
 /**
  * math.js
  * https://github.com/josdejong/mathjs
diff --git a/lib/index.js b/lib/index.js
index 08fb5fde6..5bf5cf622 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   require('./type'),        // data types (Matrix, Complex, Unit, ...)
   require('./constants'),   // constants
diff --git a/lib/json/index.js b/lib/json/index.js
index cf070ec77..009881702 100644
--- a/lib/json/index.js
+++ b/lib/json/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   require('./reviver')
 ];
diff --git a/lib/type/bignumber/BigNumber.js b/lib/type/bignumber/BigNumber.js
index 27128b0af..ec3a14bfe 100644
--- a/lib/type/bignumber/BigNumber.js
+++ b/lib/type/bignumber/BigNumber.js
@@ -1,3 +1,4 @@
+'use strict';
 var Decimal = require('decimal.js/decimal.js'); // make sure to pick the es5 version
 
 function factory (type, config, load, typed, math) {
@@ -45,4 +46,4 @@ function factory (type, config, load, typed, math) {
 exports.name = 'BigNumber';
 exports.path = 'type';
 exports.factory = factory;
-exports.math = true; // request access to the math namespace
\ No newline at end of file
+exports.math = true; // request access to the math namespace
diff --git a/lib/type/bignumber/index.js b/lib/type/bignumber/index.js
index fbd9c4a0f..e1e61a8cf 100644
--- a/lib/type/bignumber/index.js
+++ b/lib/type/bignumber/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   // type
   require('./BigNumber'),
diff --git a/lib/type/chain/index.js b/lib/type/chain/index.js
index a85eacb1b..ac7c5f099 100644
--- a/lib/type/chain/index.js
+++ b/lib/type/chain/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   // type
   require('./Chain'),
diff --git a/lib/type/complex/Complex.js b/lib/type/complex/Complex.js
index befa2666d..d9362c46c 100644
--- a/lib/type/complex/Complex.js
+++ b/lib/type/complex/Complex.js
@@ -1,3 +1,4 @@
+'use strict';
 var Complex = require('complex.js');
 var format = require('../../utils/number').format;
 var isNumber = require('../../utils/number').isNumber;
diff --git a/lib/type/complex/index.js b/lib/type/complex/index.js
index d434aeb18..3aa4ee640 100644
--- a/lib/type/complex/index.js
+++ b/lib/type/complex/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   // type
   require('./Complex'),
diff --git a/lib/type/fraction/Fraction.js b/lib/type/fraction/Fraction.js
index 9d8417ccd..a24884cac 100644
--- a/lib/type/fraction/Fraction.js
+++ b/lib/type/fraction/Fraction.js
@@ -1,3 +1,4 @@
+'use strict';
 var Fraction = require('fraction.js');
 
 /**
diff --git a/lib/type/fraction/index.js b/lib/type/fraction/index.js
index cecc7249b..c9d6b14f4 100644
--- a/lib/type/fraction/index.js
+++ b/lib/type/fraction/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   // type
   require('./Fraction'),
diff --git a/lib/type/index.js b/lib/type/index.js
index edbe84969..9df19c6e6 100644
--- a/lib/type/index.js
+++ b/lib/type/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   require('./bignumber'),
   require('./boolean'),
diff --git a/lib/type/matrix/index.js b/lib/type/matrix/index.js
index 69a9d19f6..f5866f41c 100644
--- a/lib/type/matrix/index.js
+++ b/lib/type/matrix/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   // types
   require('./Matrix'),
diff --git a/lib/type/resultset/index.js b/lib/type/resultset/index.js
index 2ca7e682f..a3e9b697c 100644
--- a/lib/type/resultset/index.js
+++ b/lib/type/resultset/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   // type
   require('./ResultSet')
diff --git a/lib/type/unit/index.js b/lib/type/unit/index.js
index 23a1273d0..fad5317ba 100644
--- a/lib/type/unit/index.js
+++ b/lib/type/unit/index.js
@@ -1,3 +1,4 @@
+'use strict';
 module.exports = [
   // type
   require('./Unit'),
diff --git a/lib/type/unit/physicalConstants.js b/lib/type/unit/physicalConstants.js
index e1c60c2cb..0ab35b47b 100644
--- a/lib/type/unit/physicalConstants.js
+++ b/lib/type/unit/physicalConstants.js
@@ -1,3 +1,4 @@
+'use strict';
 var lazy = require('../../utils/object').lazy;
 
 
diff --git a/lib/utils/bignumber/bitAnd.js b/lib/utils/bignumber/bitAnd.js
index 9f98536aa..bd31aeb2d 100644
--- a/lib/utils/bignumber/bitAnd.js
+++ b/lib/utils/bignumber/bitAnd.js
@@ -1,3 +1,4 @@
+'use strict';
 var bitwise = require('./bitwise');
 
 /**
diff --git a/lib/utils/bignumber/bitNot.js b/lib/utils/bignumber/bitNot.js
index bb69eee7a..fdcceb525 100644
--- a/lib/utils/bignumber/bitNot.js
+++ b/lib/utils/bignumber/bitNot.js
@@ -1,3 +1,4 @@
+'use strict';
 /**
  * Bitwise not
  * @param {BigNumber} value
diff --git a/lib/utils/bignumber/bitOr.js b/lib/utils/bignumber/bitOr.js
index d1ae8b696..2c4158f04 100644
--- a/lib/utils/bignumber/bitOr.js
+++ b/lib/utils/bignumber/bitOr.js
@@ -1,3 +1,4 @@
+'use strict';
 var bitwise = require('./bitwise');
 
 /**
diff --git a/lib/utils/bignumber/bitXor.js b/lib/utils/bignumber/bitXor.js
index 647740f60..144bb122a 100644
--- a/lib/utils/bignumber/bitXor.js
+++ b/lib/utils/bignumber/bitXor.js
@@ -1,3 +1,4 @@
+'use strict';
 var bitwise = require('./bitwise');
 var bitNot = require('./bitNot');
 
diff --git a/lib/utils/bignumber/bitwise.js b/lib/utils/bignumber/bitwise.js
index 3d3b85020..b147c141f 100644
--- a/lib/utils/bignumber/bitwise.js
+++ b/lib/utils/bignumber/bitwise.js
@@ -1,3 +1,4 @@
+'use strict';
 var bitNot = require('./bitNot');
 
 /**
diff --git a/lib/utils/bignumber/constants.js b/lib/utils/bignumber/constants.js
index fb4190a07..1dc8e624c 100644
--- a/lib/utils/bignumber/constants.js
+++ b/lib/utils/bignumber/constants.js
@@ -1,3 +1,4 @@
+'use strict';
 var memoize = require('../function').memoize;
 
 /**
diff --git a/lib/utils/bignumber/formatter.js b/lib/utils/bignumber/formatter.js
index 08c99517e..748207aac 100644
--- a/lib/utils/bignumber/formatter.js
+++ b/lib/utils/bignumber/formatter.js
@@ -1,3 +1,4 @@
+'use strict';
 /**
  * Convert a BigNumber to a formatted string representation.
  *
diff --git a/lib/utils/bignumber/isBigNumber.js b/lib/utils/bignumber/isBigNumber.js
index d6681572a..d32d713fb 100644
--- a/lib/utils/bignumber/isBigNumber.js
+++ b/lib/utils/bignumber/isBigNumber.js
@@ -1,3 +1,4 @@
+'use strict';
 /**
  * Test whether a value is a BigNumber
  * @param {*} x
diff --git a/lib/utils/bignumber/leftShift.js b/lib/utils/bignumber/leftShift.js
index a9451be00..d76b403f7 100644
--- a/lib/utils/bignumber/leftShift.js
+++ b/lib/utils/bignumber/leftShift.js
@@ -1,3 +1,4 @@
+'use strict';
 
 /**
  * Bitwise left shift
diff --git a/lib/utils/bignumber/rightArithShift.js b/lib/utils/bignumber/rightArithShift.js
index aa01bbc99..ce4ab63ab 100644
--- a/lib/utils/bignumber/rightArithShift.js
+++ b/lib/utils/bignumber/rightArithShift.js
@@ -1,3 +1,4 @@
+'use strict';
 /*
  * Special Cases:
  *   n >> -n =  N
diff --git a/lib/utils/emitter.js b/lib/utils/emitter.js
index 9af10b0be..81f76c531 100644
--- a/lib/utils/emitter.js
+++ b/lib/utils/emitter.js
@@ -1,3 +1,4 @@
+'use strict';
 var Emitter = require('tiny-emitter');
 
 /**
diff --git a/lib/utils/function.js b/lib/utils/function.js
index 5750f0522..92029c1eb 100644
--- a/lib/utils/function.js
+++ b/lib/utils/function.js
@@ -1,3 +1,4 @@
+'use strict';
 // function utils
 
 /**