diff --git a/javascript/lib/data-structures/chapter-1/1_4.js b/javascript/lib/data-structures/chapter-1/1_4.js
new file mode 100644
index 00000000..710eee97
--- /dev/null
+++ b/javascript/lib/data-structures/chapter-1/1_4.js
@@ -0,0 +1,38 @@
+module.exports = Strings_1_4 = (function() {
+  return {
+    // Replace spaces to %20 in the given string.
+    // @param {String} str
+    // @retuns {String} - string with replaced spaces
+    replaceSpaces: function(str) {
+      var strArr = [],
+        strLen = str.length,
+        spaceCount = 0,
+        newLength,
+        i = 0;
+
+      for (;i < strLen; i++) {
+        strArr[i] = str.charAt(i);
+        
+        if (strArr[i] === ' ') {
+          spaceCount++;
+        } 
+      }
+      
+      newLength = strLen + 2*spaceCount;
+      
+      for (i = strLen - 1; i >= 0; i--) {
+        if (strArr[i] === ' ') {
+          strArr[newLength - 1] = '0';
+          strArr[newLength - 2] = '2';
+          strArr[newLength - 3] = '%';
+          newLength = newLength - 3;
+        } else {
+          strArr[newLength - 1] = str[i];
+          newLength = newLength - 1;
+        }
+      }
+
+      return strArr.join('');
+    }
+  };
+}());
diff --git a/javascript/lib/data-structures/chapter-1/1_5.js b/javascript/lib/data-structures/chapter-1/1_5.js
new file mode 100644
index 00000000..c9ceeea9
--- /dev/null
+++ b/javascript/lib/data-structures/chapter-1/1_5.js
@@ -0,0 +1,69 @@
+module.exports = Strings_1_5 = (function() {
+  return {
+    // Compress string.
+    // Solution with arrays without string concatenation. Should be theoretically faster.
+    // @param {String} str - input string
+    // @retuns {String} - compressed string
+    compressString: function compressString(str) {
+      var compressedStringLength = countCompressedStringLength(str),
+          compressedCharArray,
+          compressedCharArrayIndex = 0,
+          previousSymbol = str[0],
+          previousSymbolCount = 1,
+          currentSymbol,
+          i;
+
+      if (compressedStringLength >= str.length) {
+        return str;
+      }
+
+      compressedCharArray = new Array(compressedStringLength);
+
+      for (i = 1; i < str.length; i++) {
+        currentSymbol = str.charAt(i);
+
+        if (currentSymbol === previousSymbol) {
+          previousSymbolCount++;
+        } else {
+          compressedCharArray[compressedCharArrayIndex++] = previousSymbol;
+          compressedCharArray[compressedCharArrayIndex++] = previousSymbolCount;
+          previousSymbol = currentSymbol;
+          previousSymbolCount = 1;
+        }
+      }
+
+      compressedCharArray[compressedCharArrayIndex++] = previousSymbol;
+      compressedCharArray[compressedCharArrayIndex] = previousSymbolCount;
+
+      return compressedCharArray.join('');
+
+      function countCompressedStringLength(str) {
+        if (typeof str === 'undefined' || str === null || str === '') {
+          return 0;
+        }
+
+        var previousSymbol = str[0],
+            previousSymbolCount = 1,
+            currentSymbol,
+            compressedStringLength = 0,
+            i;
+
+        for (i = 1; i < str.length; i++) {
+          currentSymbol = str.charAt(i);
+
+          if (currentSymbol === previousSymbol) {
+            previousSymbolCount++;
+          } else {
+            compressedStringLength += (1 + previousSymbolCount.toString().length);
+            previousSymbol = currentSymbol;
+            previousSymbolCount = 1;
+          }
+        }
+
+        compressedStringLength += (1 + previousSymbolCount.toString().length);
+
+        return compressedStringLength;
+      }
+    }
+  };
+}());
diff --git a/javascript/lib/data-structures/chapter-1/1_6.js b/javascript/lib/data-structures/chapter-1/1_6.js
new file mode 100644
index 00000000..ea31235a
--- /dev/null
+++ b/javascript/lib/data-structures/chapter-1/1_6.js
@@ -0,0 +1,40 @@
+module.exports = Strings_1_6 = (function() {
+  return {
+    /**
+     * Rotate grid by 90 degrees. Grid is assumed to be NxN size.
+     * @param {Number[][]} grid - two-dimensional array of size NxN
+     */
+    rotate: function rotate(grid) {
+      var N = grid.length,
+          layer,
+          i,
+          offset,
+          first,
+          last,
+          top;
+
+      for (layer = 0; layer < Math.floor(N / 2); ++layer) {
+        first = layer;
+        last = N - 1 - layer;
+
+        for(i = first; i < last; ++i) {
+          offset = i - first;
+          
+          top = grid[first][i]; // save top
+
+          // left -> top
+          grid[first][i] = grid[last-offset][first];
+
+          // bottom -> left
+          grid[last-offset][first] = grid[last][last - offset];
+
+          // right -> bottom
+          grid[last][last - offset] = grid[i][last];
+
+          // top -> right
+          grid[i][last] = top; // right <- saved top
+        }
+      }
+    }
+  };
+}());
diff --git a/javascript/test/data-structures/chapter-1/1_4_Spec.js b/javascript/test/data-structures/chapter-1/1_4_Spec.js
new file mode 100644
index 00000000..dae7f434
--- /dev/null
+++ b/javascript/test/data-structures/chapter-1/1_4_Spec.js
@@ -0,0 +1,8 @@
+require('../../test_helper');
+describe(Strings_1_4, function () {
+  describe('replaceSpaces', function () {
+    it('knows how to replace spaces', function () {
+      expect(Strings_1_4.replaceSpaces(' abcdef  gh  ')).to.equal('%20abcdef%20%20gh%20%20');
+    });
+  });
+});
diff --git a/javascript/test/data-structures/chapter-1/1_5_Spec.js b/javascript/test/data-structures/chapter-1/1_5_Spec.js
new file mode 100644
index 00000000..7907b1d3
--- /dev/null
+++ b/javascript/test/data-structures/chapter-1/1_5_Spec.js
@@ -0,0 +1,11 @@
+require('../../test_helper');
+describe('Strings_1_5', function () {
+  describe('compressString', function () {
+    it('returns compressed string when it is smaller than original one', function () {
+      expect(Strings_1_5.compressString('aabcccccaaa')).to.equal('a2b1c5a3');
+    });
+    it('returns original string when it is not smaller than original one', function () {
+      expect(Strings_1_5.compressString('aabb')).to.equal('aabb');
+    });
+  });
+});
diff --git a/javascript/test/data-structures/chapter-1/1_6_Spec.js b/javascript/test/data-structures/chapter-1/1_6_Spec.js
new file mode 100644
index 00000000..da50b882
--- /dev/null
+++ b/javascript/test/data-structures/chapter-1/1_6_Spec.js
@@ -0,0 +1,22 @@
+require('../../test_helper');
+describe('Strings_1_6', function () {
+  describe('rotate', function () {
+    it('rotates two-dimensional array by 90 degrees', function () {
+      var grid = [
+        [1,2,3,4],
+        [5,6,7,8],
+        [9,10,11,12],
+        [13,14,15,16]
+      ];
+
+      Strings_1_6.rotate(grid);
+
+      expect(grid).to.deep.equal([
+        [13,9,5,1],
+        [14,10,6,2],
+        [15,11,7,3],
+        [16,12,8,4]
+      ]);
+    });
+  });
+});