仓库源文，站点原文

title: Some tips about learning JavaScript layout: post thread: 161 date: 2015-08-28 author: Joe Jiang categories: Document tags: [JavaScript]

excerpt: When I had my internship in DeepGlint, my supervisor gave me a lot of advice about how to obtain the ability to develop the interesting web world.

JS对象

• ECMAScript中5种简单数据类型（基本数据类型）: Undefined、Null、Boolean、Number和String, 1种复杂数据类型: Object;
• typeof是一个操作符而不是函数, 对未初始化和未声明的变量执行typeof操作符都会返回undefined值;
• Null类型只有一个值, null;
• 永远不要测试某个特定的浮点数值，浮点数值的最高精度是17位小数，但在进行算术计算时其精确度远远不如整数。例如，0.1加0.2的结果不是0.3，而是0.30000000000000004;
• 计算结果超出JavaScript数值范围的值会表示为Infinity或者-Infinity;
• NaN数值用于表示一个本来要返回数值的操作数未返回数值的情况，NaN还具有以下特性：任何涉及NaN的操作均返回NaN，NaN和任何数值都不相等;
• for-in语句是一种精准的迭代语句，可以用来枚举对象的属性;
• switch语句在比较值时使用的是全等操作符;

一些有用的函数

• Boolean() //将一个值转换为其对应的Boolean值;
• Number.MIN_VALUE / Number.MAX_VALUE //分别代表ECMAScript中能表示的数值最小值和最大值;
• isFinite() //查看数值是否无穷，返回true或者false;
• isNaN() //查看结果是否不是数值;
• 把非数值转化为数值的函数：Number()、parseInt()和parseFloat()，第一个函数，即转型函数Number()可以用于任何数据类型，而另两个函数则专门用于把字符串转换成数值;

Attention: parseInt 允许我们自定义接受参数的进制格式.比如以0开头的字符串很少会被用于八进制格式化(特别是在用户输入中). 为了处理这类问题, parseInt 接受第二个参数,基数.它可以指出第一个字符串参数要被如何解析.特别指出,第二个参数如果是 10 , parseInt 函数将解析第一参数字符串只能为十进制，例如parseInt(col, 10)

• valueOf() // 返回对象的初始值;
• 把一个值转换为一个字符串有两种方式: 使用值的toString()方法; 使用转型函数String()，该函数能够将任何类型的值转换为字符串;
• result = variable instanceof constructor // 查看variable是否为constructor类型;

JavaScript 秘密花园

• hasOwnProperty 是 JavaScript 中唯一一个处理属性但是不查找原型链的函数。
• 和 in 操作符一样，for in 循环同样在查找对象属性时遍历原型链上的所有属性。

Others

The most important four elements in understanding JavaScript are:

• Callback Function
• Scoping
• Anonymous functions
• Object

There's really a lot of resource when you Google how to understand them, so I do not repeat them here. Then follows two links about how to learn them well in a better way, the first website is JavaScript: The Right Way. The content covers a guide intended to introduce new developers to JavaScript and help experienced developers learn more about its best practices, such as JavaScript Code Style, design patterns contained in JavaScript, some frameworks, game engines, etc. The website may not explain the points that mentioned in it specifically, but it really gives people a good direction in how to understand and learn JavaScript deeply.

The second link I want to share is Principles of Writing Consistent, Idiomatic JavaScript. It is a document about how to write consistent, idiomatic JavaScript in our daily life. It provides many translated versions for different kinds of people around the world.