前端面试题

Javascript问题集锦

1. 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.

2. 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

3. 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】

来源

1. https://github.com/creeperyang/blog/issues/2