前端面试题

来源：creeperyang/blog#2

Javascript问题集锦

对象字面值不能正常解析

问题：
```
{a:1}.a;//Uncaught SyntaxError:Unexpected token
```
解决：
```
({a:1}).a;
({a:1}.a)
```
原因：

An object literal is a list of zero or more pairs of property names and associated values of an object, enclosed in curly braces ({}). You should not use an object literal at the beginning of a statement. This will lead to an error or not behave as you expect, because the { will be interpreted as the beginning of a block.

数字的点操作符

问题：

123.toFixed(2); //Uncaught SyntaxError: Unexpected token ILLEGAL

解决：

(123).toFixed(2);
//以下两种都可以，不推荐
123..toFixed(2);
123 .toFixed(2)

原因：

js解析器把数字后的当作小数点而不是点操作

连续赋值问题

问题：尝试解释下连等赋值的过程
```
var a = {n:1};
var b = a;
a.x = a = {n:2};
console.log(a.x); //undefined
console.log(b.x); //{n:2}
```
原因：
1. 执行顺序。a.x = a = {n:2}相当于是a.x = (a = {n:2})，也就是先执行a = {n:2}，再执行a.x = {n:2};
2. 执行时，a.x和a的指向都是对象{n:1}【关键】