JavaScript Learning Notes 1 data Types _ Basics

Only one form of code type is a function.

Undefined: Undefined, we can also call it non-existent, typeof (undefined) =undefined.

Null: null. Undefined is non-existent, and Null is present, but none. typeof (null) =object, but null is not object, which is the magic and uniqueness of NULL.

Boolean:true or False.

Number:nan and Infinity are two special numbers, and Nan represents a number that cannot be represented by a number, while the infinity represents an infinite number, and in contrast, the-infinify represents negative infinity. Here are two special places: Nan!=nan,infinity/infinity=nan. In the number type, there is a very useful method: ToString (), he can accept a digit from 2 to 36, and then convert our number to the corresponding binary.

String: Strings, the concept of no characters in JavaScript, and the string is the smallest unit representing text. In a string, there are two functions such as Charat (index) and charCodeAt (index) that return the character and character Unicode encoding of the corresponding index, respectively. In our peacetime, may often use the subscript way to visit, such as s[10], but this is not ECMAScript standard, should try to avoid.

All types of JavaScript are built up based on these five simple types. There is a myriad of complex relationships between these five types, and undefined,null,0, "" is false when converted to Boolean, and all of these four are true. But among these five, except Undefined==null, the others are not equal.

Here again we have this and strongly typed language, such as 123== "123". So how can we distinguish between types? This time: all equal: = = = To play a useful role.