Merge pull request #133 from tao363/master

Update array stack

codes/typescript/chapter_stack_and_queue/array_stack.ts

@@ -11,6 +11,7 @@ class ArrayStack {
     constructor() {
         this.stack = [];
     }
+
     /* 获取栈的长度 */
     get size(): number {
         return this.stack.length;
@@ -28,16 +29,19 @@ class ArrayStack {
 
     /* 出栈 */
     pop(): number | undefined {
+        if (this.empty()) throw new Error('栈为空');
         return this.stack.pop();
     }
 
     /* 访问栈顶元素 */
     top(): number | undefined {
+        if (this.empty()) throw new Error('栈为空');
         return this.stack[this.stack.length - 1];
     }
 
     /* 访问索引 index 处元素 */
     get(index: number): number | undefined {
+        if (index >= this.size) throw new Error('索引越界');
         return this.stack[index];
     }
 
@@ -83,4 +87,4 @@ console.log("栈的长度 size = " + size);
 const empty = stack.empty();
 console.log("栈是否为空 = " + empty);
 
-export { };
+export { };