一开始认为在循环内定义变量是不明智的行为，所以会尽量把定义变量放到循环外，但导致语义不清，很难看懂。所以现在是以考虑变量的作用域和语义作为优先因素

fa-ge · fa-ge · commit 2d0bbf9115df · 2016-11-07T16:03:13.000+08:00
diff --git a/102-Binary-Tree-Level-Order-Traversal/index.js b/102-Binary-Tree-Level-Order-Traversal/index.js
@@ -16,10 +16,9 @@ var levelOrder = function(root) {
 
     let queue = [root]
     const res = []
-    let tmpQueue
     let n = 0
     while (queue.length !== 0) {
-        tmpQueue = []
+        let tmpQueue = []
         res[n] = []
         while (root = queue.shift()) {
             res[n].push(root.val)
diff --git a/103-Binary-Tree-Zigzag-Level-Order-Traversal/index.js b/103-Binary-Tree-Zigzag-Level-Order-Traversal/index.js
@@ -16,10 +16,9 @@ var zigzagLevelOrder = function(root) {
 
     let queue = [root]
     const res = []
-    let tmpQueue
     let n = 0
     while (queue.length !== 0) {
-        tmpQueue = []
+        let tmpQueue = []
         res[n] = []
         while (queue.length !== 0) {
             root = queue.shift()
diff --git a/107-Binary-Tree-Level-Order-Traversal-II/index.js b/107-Binary-Tree-Level-Order-Traversal-II/index.js
@@ -15,11 +15,10 @@ var levelOrderBottom = function(root) {
     }
     const res = []
     let queue = [root]
-    let tmpQueue = []
 
     let n = 0
     while (queue.length !== 0) {
-        tmpQueue = []
+        let tmpQueue = []
         res[n] = []
         while (root = queue.shift()) {
             res[n].push(root.val)
diff --git a/111-Minimum-Depth-of-Binary-Tree/index.js b/111-Minimum-Depth-of-Binary-Tree/index.js
@@ -15,9 +15,8 @@ var minDepth = function(root) {
     }
     let queue = [root]
     let n = 0
-    let tmpQueue
     while (queue.length !== 0) {
-        tmpQueue = []
+        let tmpQueue = []
         while (root = queue.pop()) {
             if (root.left || root.right) {
                 root.left && tmpQueue.push(root.left)
diff --git a/145-Binary-Tree-Postorder-Traversal/index.js b/145-Binary-Tree-Postorder-Traversal/index.js
@@ -13,13 +13,12 @@ var postorderTraversal = function(root) {
     const stack = []
     const res = []
 
-    let stackTop
     while (stack.length !== 0 || root) {
         while (root && !root.isVisited) {
             stack.push(root)
             root = root.left
         }
-        stackTop = stack[stack.length - 1]
+        let stackTop = stack[stack.length - 1]
         if (!stackTop) {
             break
         }
diff --git a/199-Binary-Tree-Right-Side-View/index.js b/199-Binary-Tree-Right-Side-View/index.js
@@ -17,9 +17,8 @@ var rightSideView = function(root) {
     }
 
     let queue = [root]
-    let tmpQueue
     while (queue.length !== 0) {
-        tmpQueue = []
+        let tmpQueue = []
         for (let i = 0, len = queue.length; i < len; i++) {
             root = queue.shift()
             if (i === 0) {
diff --git a/2-Add-Two-Numbers/index.js b/2-Add-Two-Numbers/index.js
@@ -38,13 +38,11 @@ function ListNode(val) {
 var addTwoNumbers = function(l1, l2) {
     let tail
     let head
-    let res
     let carry = 0
-    let sum = 0
     while (l1 || l2 || carry) {
-        sum = carry + (l1 ? l1.val : 0) + (l2 ? l2.val : 0)
+        let sum = carry + (l1 ? l1.val : 0) + (l2 ? l2.val : 0)
         carry = Math.floor(sum / 10)
-        res = new ListNode(sum % 10)
+        let res = new ListNode(sum % 10)
         if (!head) {
             head = res
             tail = res
diff --git a/240-Search-a-2D-Matrix II/index.js b/240-Search-a-2D-Matrix II/index.js
@@ -7,9 +7,8 @@ var searchMatrix = function(matrix, target) {
     function bSearch(arr, target) {
         let low = 0
         let high = arr.length - 1
-        let mid
         while (low <= high) {
-            mid = Math.floor((low + high) / 2)
+            let mid = Math.floor((low + high) / 2)
             if (target > arr[mid]) {
                 low = mid + 1
             } else if (target < arr[mid]) {
diff --git a/35-Search-Insert-Position/index.js b/35-Search-Insert-Position/index.js
@@ -6,9 +6,8 @@
 function bSearchRange(arr, target) {
     let low = 0
     let high = arr.length - 1
-    let mid
     while (low <= high) {
-        mid = Math.floor((low + high) / 2)
+        let mid = Math.floor((low + high) / 2)
         if (target > arr[mid]) {
             low = mid + 1
         } else if (target < arr[mid]) {
diff --git a/371-Sum-of-Two-Integers/index.js b/371-Sum-of-Two-Integers/index.js
@@ -4,9 +4,8 @@
  * @return {number}
  */
 var getSum = function(a, b) {
-    let res = 0
     while (b !== 0) {
-        res = a ^ b
+        let res = a ^ b
         b = (b & a) << 1
         a = res
     }
diff --git a/74-Search-a-2D-Matrix/index.js b/74-Search-a-2D-Matrix/index.js
@@ -22,9 +22,8 @@
 function bSearch(arr, target) {
     let low = 0
     let high = arr.length - 1
-    let mid
     while (low <= high) {
-        mid = Math.floor((low + high) / 2)
+        let mid = Math.floor((low + high) / 2)
         if (target > arr[mid]) {
             low = mid + 1
         } else if (target < arr[mid]) {
diff --git a/74-Search-a-2D-Matrix/index2.js b/74-Search-a-2D-Matrix/index2.js
@@ -7,9 +7,8 @@
 function bSearchRange(arr, target) {
     let low = 0
     let high = arr.length - 1
-    let mid
     while (low <= high) {
-        mid = Math.floor((low + high) / 2)
+        let mid = Math.floor((low + high) / 2)
         if (target > arr[mid]) {
             low = mid + 1
         } else if (target < arr[mid]) {
@@ -24,9 +23,8 @@ function bSearchRange(arr, target) {
 function bSearch(arr, target) {
     let low = 0
     let high = arr.length - 1
-    let mid
     while (low <= high) {
-        mid = Math.floor((low + high) / 2)
+        let mid = Math.floor((low + high) / 2)
         if (target > arr[mid]) {
             low = mid + 1
         } else if (target < arr[mid]) {
diff --git a/94-Binary-Tree-Inorder-Traversal/index.js b/94-Binary-Tree-Inorder-Traversal/index.js
@@ -12,15 +12,14 @@
 var inorderTraversal = function(root) {
     const stack = []
     const res = []
-    let tmp
 
     while (root || stack.length !== 0) {
         while (root) {
             stack.push(root)
             root = root.left
         }
 
-        tmp = stack.pop()
+        let tmp = stack.pop()
         res.push(tmp.val)
         root = tmp.right
     }

Original file line number	Diff line number	Diff line change
`@@ -13,13 +13,12 @@ var postorderTraversal = function(root) {`
`13`	`13`	`const stack = []`
`14`	`14`	`const res = []`
`15`	`15`
`16`		`- let stackTop`
`17`	`16`	`while (stack.length !== 0 \|\| root) {`
`18`	`17`	`while (root && !root.isVisited) {`
`19`	`18`	`stack.push(root)`
`20`	`19`	`root = root.left`
`21`	`20`	`}`
`22`		`- stackTop = stack[stack.length - 1]`
	`21`	`+ let stackTop = stack[stack.length - 1]`
`23`	`22`	`if (!stackTop) {`
`24`	`23`	`break`
`25`	`24`	`}`