diff --git a/vlib/builtin/js/map.js.v b/vlib/builtin/js/map.js.v
index 894d614cf0..033a5fde9e 100644
--- a/vlib/builtin/js/map.js.v
+++ b/vlib/builtin/js/map.js.v
@@ -14,3 +14,13 @@ pub fn (mut m map) delete(key voidptr) {
 pub fn (m &map) free() {}
 
 #map.prototype[Symbol.iterator] = function () { return this.map[Symbol.iterator](); }
+
+#map.prototype.toString = function () {
+#function fmtKey(key) { return typeof key == 'string' ? '\'' + key + '\'' : key}
+#let res = '{'
+#for (const entry of this) {
+#res += fmtKey(entry[0]) + ': ' + entry[0];
+#}
+#res += '}'
+#return res;
+#}
diff --git a/vlib/builtin/js/string.js.v b/vlib/builtin/js/string.js.v
index e7d270800d..f209fb8d6d 100644
--- a/vlib/builtin/js/string.js.v
+++ b/vlib/builtin/js/string.js.v
@@ -94,7 +94,10 @@ pub fn (s string) count(substr string) int {
 }
 
 pub fn (s string) ends_with(p string) bool {
-	return s.str.endsWith(p.str)
+	mut res := false
+	#res.val = s.str.endsWith(p.str)
+
+	return res
 }
 
 pub fn (s string) starts_with(p string) bool {
@@ -133,7 +136,7 @@ pub fn (s string) fields() []string {
 }
 
 pub fn (s string) find_between(start string, end string) string {
-	return string(s.str.slice(s.str.indexOf(start.str), s.str.indexOf(end.str) + 1))
+	return string(s.str.slice(s.str.indexOf(start.str) + 1, s.str.indexOf(end.str)))
 }
 
 // unnecessary in the JS backend, implemented for api parity.
@@ -464,3 +467,77 @@ pub fn (s string) strip_margin_custom(del byte) string {
 
 	return result
 }
+
+// split_nth splits the string based on the passed `delim` substring.
+// It returns the first Nth parts. When N=0, return all the splits.
+// The last returned element has the remainder of the string, even if
+// the remainder contains more `delim` substrings.
+[direct_array_access]
+pub fn (s string) split_nth(delim string, nth int) []string {
+	mut res := []string{}
+	mut i := 0
+
+	match delim.len {
+		0 {
+			i = 1
+			for ch in s {
+				if nth > 0 && i >= nth {
+					res << s[i..]
+					break
+				}
+				res << ch.str()
+				i++
+			}
+			return res
+		}
+		1 {
+			mut start := 0
+			delim_byte := delim[0]
+
+			for i < s.len {
+				if s[i] == delim_byte {
+					was_last := nth > 0 && res.len == nth - 1
+					if was_last {
+						break
+					}
+					val := s[start..i] //.substr(start, i)
+					res << val
+					start = i + delim.len
+					i = start
+				} else {
+					i++
+				}
+			}
+
+			// Then the remaining right part of the string
+			if nth < 1 || res.len < nth {
+				res << s[start..]
+			}
+			return res
+		}
+		else {
+			mut start := 0
+			// Take the left part for each delimiter occurence
+			for i <= s.len {
+				is_delim := i + delim.len <= s.len && s[i..i + delim.len] == delim
+				if is_delim {
+					was_last := nth > 0 && res.len == nth - 1
+					if was_last {
+						break
+					}
+					val := s[start..i] // .substr(start, i)
+					res << val
+					start = i + delim.len
+					i = start
+				} else {
+					i++
+				}
+			}
+			// Then the remaining right part of the string
+			if nth < 1 || res.len < nth {
+				res << s[start..]
+			}
+			return res
+		}
+	}
+}
diff --git a/vlib/v/gen/js/builtin_types.v b/vlib/v/gen/js/builtin_types.v
index 0b16fc006c..69158dd568 100644
--- a/vlib/v/gen/js/builtin_types.v
+++ b/vlib/v/gen/js/builtin_types.v
@@ -30,7 +30,7 @@ fn (mut g JsGen) to_js_typ_val(t ast.Type) string {
 			styp = '$prefix${g.sym_to_js_typ(sym)}("")'
 		}
 		.map {
-			styp = 'new Map()'
+			styp = 'new map(new Map())'
 		}
 		.array {
 			styp = '$prefix${g.sym_to_js_typ(sym)}()'
@@ -335,6 +335,7 @@ fn (mut g JsGen) gen_builtin_type_defs() {
 					typ_name: typ_name
 					default_value: 'new Boolean(false)'
 					to_jsval: '+this != 0'
+					eq: 'this.val === other.valueOf()'
 				)
 			}
 			'string' {
@@ -354,7 +355,7 @@ fn (mut g JsGen) gen_builtin_type_defs() {
 				g.gen_builtin_prototype(
 					typ_name: typ_name
 					val_name: 'map'
-					default_value: 'new Map()'
+					default_value: 'new map(new Map())'
 					constructor: 'this.map = map'
 					value_of: 'this'
 					to_string: 'this.map.toString()'
diff --git a/vlib/v/gen/js/js.v b/vlib/v/gen/js/js.v
index aabca09738..9778b44944 100644
--- a/vlib/v/gen/js/js.v
+++ b/vlib/v/gen/js/js.v
@@ -1831,17 +1831,16 @@ fn (mut g JsGen) gen_infix_expr(it ast.InfixExpr) {
 	} else {
 		is_arithmetic := it.op in [token.Kind.plus, .minus, .mul, .div, .mod]
 
-		mut needs_cast := is_arithmetic && it.left_type != it.right_type
 		mut greater_typ := 0
 		// todo(playX): looks like this cast is always required to perform .eq operation on types.
-		if true || needs_cast {
+		if is_arithmetic {
 			greater_typ = g.greater_typ(it.left_type, it.right_type)
 			if g.cast_stack.len > 0 {
-				needs_cast = g.cast_stack.last() != greater_typ
+				// needs_cast = g.cast_stack.last() != greater_typ
 			}
 		}
 
-		if true || needs_cast {
+		if is_arithmetic {
 			if g.ns.name == 'builtin' {
 				g.write('new ')
 			}
@@ -1855,7 +1854,7 @@ fn (mut g JsGen) gen_infix_expr(it ast.InfixExpr) {
 
 		g.expr(it.right)
 
-		if true || needs_cast {
+		if is_arithmetic {
 			g.cast_stack.delete_last()
 			g.write(')')
 		}
diff --git a/vlib/v/gen/js/tests/testdata/array.out b/vlib/v/gen/js/tests/testdata/array.out
index 3ab514deaf..c152476d81 100644
--- a/vlib/v/gen/js/tests/testdata/array.out
+++ b/vlib/v/gen/js/tests/testdata/array.out
@@ -195,6 +195,7 @@ true
 [2, 3, 4]
 [1, 2, 3]
 [1, 2, 3]
+[[1, 2, 3], [4, 5, 6]]
 true
 true
 true
@@ -292,5 +293,11 @@ true
 true
 true
 0
+`exists`: true and `not exists`: false
 [[], [], [], []]
 [[], [], [123], []]
+[{}, {}, {}, {}]
+[{}, {}, {'123': 123}, {}]
+Numbers { odds: [1, 3, 5] , evens: [2, 4] }
+Numbers { odds: [3, 5, 7] , evens: [2, 6, 10] }
+[[10, 10, 10], [10, 10, 10], [10, 10, 10]]
diff --git a/vlib/v/gen/js/tests/testdata/array.v b/vlib/v/gen/js/tests/testdata/array.v
index 2465669f26..de669b3374 100644
--- a/vlib/v/gen/js/tests/testdata/array.v
+++ b/vlib/v/gen/js/tests/testdata/array.v
@@ -16,6 +16,11 @@ struct Coord {
 	z int
 }
 
+struct Numbers {
+	odds  []int
+	evens []int
+}
+
 struct Person {
 	name string
 	nums []int
@@ -672,15 +677,13 @@ fn main() {
 	}
 	{
 		// test array str
-		// todo(playX): JS array formatting should match what default builtin impl has.
-		/*
+
 		numbers := [1, 2, 3]
 		assert numbers == [1, 2, 3]
 		numbers2 := [numbers, [4, 5, 6]] // dup str() bug
 		println(numbers2)
 		assert true
 		assert numbers.str() == '[1, 2, 3]'
-		*/
 	}
 	{
 		// test eq
@@ -1110,8 +1113,7 @@ fn main() {
 	}
 	{
 		// test array struct contains
-		/*
-		todo: does not work
+
 		mut coords := []Coord{}
 		coord_1 := Coord{
 			x: 1
@@ -1124,7 +1126,6 @@ fn main() {
 		println('`exists`: $exists and `not exists`: $not_exists')
 		assert exists == true
 		assert not_exists == false
-		*/
 	}
 	{
 		// test array of array append
@@ -1133,4 +1134,47 @@ fn main() {
 		x[2] << 123 // RTE
 		println(x)
 	}
+	{
+		// test array of map insert
+		mut x := []map[string]int{len: 4}
+		println(x) // OK
+		x[2]['123'] = 123 // RTE
+		println(x)
+	}
+	{
+		// todo(playX): does not work
+		/*
+		// test multi fixed array init
+		a := [3][3]int{}
+		println(a)
+		*/
+	}
+	{
+		// test array of multi filter
+		arr := [1, 2, 3, 4, 5]
+		nums := Numbers{
+			odds: arr.filter(it % 2 == 1)
+			evens: arr.filter(it % 2 == 0)
+		}
+		println(nums)
+		assert nums.odds == [1, 3, 5]
+		assert nums.evens == [2, 4]
+	}
+	{
+		// test array of multi map
+		arr := [1, 3, 5]
+		nums := Numbers{
+			odds: arr.map(it + 2)
+			evens: arr.map(it * 2)
+		}
+		println(nums)
+		assert nums.odds == [3, 5, 7]
+		assert nums.evens == [2, 6, 10]
+	}
+	{
+		// test multi fixed array with default init
+		a := [3][3]int{init: [3]int{init: 10}}
+		println(a)
+		assert a == [[10, 10, 10]!, [10, 10, 10]!, [10, 10, 10]!]!
+	}
 }
diff --git a/vlib/v/gen/js/tests/testdata/string.out b/vlib/v/gen/js/tests/testdata/string.out
new file mode 100644
index 0000000000..4070999769
--- /dev/null
+++ b/vlib/v/gen/js/tests/testdata/string.out
@@ -0,0 +1,7 @@
+ab
+1000
+true
+true
+true
+man
+true
diff --git a/vlib/v/gen/js/tests/testdata/string.v b/vlib/v/gen/js/tests/testdata/string.v
new file mode 100644
index 0000000000..d8ecb5e434
--- /dev/null
+++ b/vlib/v/gen/js/tests/testdata/string.v
@@ -0,0 +1,200 @@
+struct Foo {
+	bar int
+mut:
+	str string
+}
+
+fn main() {
+	{
+		// test add
+		mut a := 'a'
+		a += 'b'
+		println(a)
+		a = 'a'
+		for i := 1; i < 1000; i++ {
+			a += 'b'
+		}
+		println(a.len)
+		println(a.ends_with('bbbbb'))
+		a += '123'
+		println(a.ends_with('3'))
+	}
+	{
+		// test ends with
+		a := 'browser.v'
+		println(a.ends_with('.v'))
+
+		s := 'V Programming Language'
+		assert s.ends_with('guage') == true
+		assert s.ends_with('Language') == true
+		assert s.ends_with('Programming Language') == true
+		assert s.ends_with('V') == false
+	}
+	{
+		// test between
+		s := 'hello [man] how you doing'
+		println(s.find_between('[', ']'))
+	}
+	{
+		// test compare
+		a := 'Music'
+		b := 'src'
+		println(b >= a)
+	}
+	{
+		// test lt
+		a := ''
+		b := 'a'
+		c := 'a'
+		d := 'b'
+		e := 'aa'
+		f := 'ab'
+
+		assert a < b
+		assert !(b < c)
+		assert c < d
+		assert !(d < e)
+		assert c < e
+		assert e < f
+	}
+	{
+		// test ge
+		a := 'aa'
+		b := 'aa'
+		c := 'ab'
+		d := 'abc'
+		e := 'aaa'
+		assert b >= a
+		assert c >= b
+		assert d >= c
+		assert !(c >= d)
+		assert e >= a
+	}
+	{
+		// test compare strings
+		a := 'aa'
+		b := 'aa'
+		c := 'ab'
+		d := 'abc'
+		e := 'aaa'
+		assert compare_strings(a, b) == 0
+		assert compare_strings(b, c) == -1
+		assert compare_strings(c, d) == -1
+		assert compare_strings(d, e) == 1
+		assert compare_strings(a, e) == -1
+		assert compare_strings(e, a) == 1
+	}
+	{
+		// test sort
+		mut vals := [
+			'arr',
+			'an',
+			'a',
+			'any',
+		]
+		len := vals.len
+		vals.sort()
+		assert len == vals.len
+		assert vals[0] == 'a'
+		assert vals[1] == 'an'
+		assert vals[2] == 'any'
+		assert vals[3] == 'arr'
+	}
+	{
+		// todo(playX): sort codegen
+		/*// test sort reverse
+		mut vals := [
+			'arr',
+			'an',
+			'a',
+			'any',
+		]
+		len := vals.len
+		vals.sort(b > a)
+		assert len == vals.len
+		assert vals[0] == 'a'
+		assert vals[1] == 'an'
+		assert vals[2] == 'any'
+		assert vals[3] == 'arr'*/
+	}
+	{
+		// todo: split nth
+		/*
+		a := '1,2,3'
+		assert a.split(',').len == 3
+		assert a.split_nth(',', -1).len == 3
+		assert a.split_nth(',', 0).len == 3
+		assert a.split_nth(',', 1).len == 1
+		assert a.split_nth(',', 2).len == 2
+		assert a.split_nth(',', 10).len == 3
+		b := '1::2::3'
+		assert b.split('::').len == 3
+		assert b.split_nth('::', -1).len == 3
+		assert b.split_nth('::', 0).len == 3
+		assert b.split_nth('::', 1).len == 1
+		assert b.split_nth('::', 2).len == 2
+		assert b.split_nth('::', 10).len == 3
+		c := 'ABCDEF'
+		println(c.split('').len)
+		assert c.split('').len == 6
+		assert c.split_nth('', 3).len == 3
+		assert c.split_nth('BC', -1).len == 2
+		d := ','
+		assert d.split(',').len == 2
+		assert d.split_nth('', 3).len == 1
+		assert d.split_nth(',', -1).len == 2
+		assert d.split_nth(',', 3).len == 2
+		e := ',,,0,,,,,a,,b,'
+		assert e.split(',,').len == 5
+		assert e.split_nth(',,', 3).len == 3
+		assert e.split_nth(',', -1).len == 12
+		assert e.split_nth(',', 3).len == 3
+		*/
+	}
+	{
+		// test split
+		mut s := 'volt/twitch.v:34'
+		mut vals := s.split(':')
+		assert vals.len == 2
+		assert vals[0] == 'volt/twitch.v'
+		assert vals[1] == '34'
+		// /////////
+		s = '2018-01-01z13:01:02'
+		vals = s.split('z')
+		assert vals.len == 2
+		assert vals[0] == '2018-01-01'
+		assert vals[1] == '13:01:02'
+		// //////////
+		s = '4627a862c3dec29fb3182a06b8965e0025759e18___1530207969___blue'
+		vals = s.split('___')
+		assert vals.len == 3
+		assert vals[0] == '4627a862c3dec29fb3182a06b8965e0025759e18'
+		assert vals[1] == '1530207969'
+		assert vals[2] == 'blue'
+		// /////////
+		s = 'lalala'
+		vals = s.split('a')
+		assert vals.len == 4
+		assert vals[0] == 'l'
+		assert vals[1] == 'l'
+		assert vals[2] == 'l'
+		assert vals[3] == ''
+		// /////////
+		s = 'awesome'
+		a := s.split('')
+		assert a.len == 7
+		assert a[0] == 'a'
+		assert a[1] == 'w'
+		assert a[2] == 'e'
+		assert a[3] == 's'
+		assert a[4] == 'o'
+		assert a[5] == 'm'
+		assert a[6] == 'e'
+		// /////////
+		s = 'wavy turquoise bags'
+		vals = s.split(' bags')
+		assert vals.len == 2
+		assert vals[0] == 'wavy turquoise'
+		assert vals[1] == ''
+	}
+}