Data types and variables in JavaScript

Number

JavaScript does not distinguish between integers and floating-point numbers, and is uniformly represented by number, and the following are valid number types:

// Integer 123 // floating point 0.456 // scientific notation means 1.2345x1000, equivalent to 1234.5 // Negative number // Nan means not a number, which is represented by Nan when the result cannot be evaluated // Infinity is infinitely large, and is represented as infinity when the value exceeds the maximum value that JavaScript can represent.

Number can do arithmetic directly, and the rules and math are consistent:

// 3 // 7.5 // Infinity // NaN // 1 // 1.5

Note that % the remainder operation is calculated.

String

strings are arbitrary text enclosed in single quotes ' or double quotes, for example, and ‘abc‘ "xyz" so on. Note that ‘‘ or "" itself is just a representation, not part of a string, so the string is ‘abc‘ only a , b c this 3 characters.

Boolean value

A Boolean value is exactly the same as a Boolean algebra, with a Boolean value of only true false two values, either, either directly, by means of a true false true false Boolean, or by a Boolean operation.

null and undefined

nullRepresents an "empty" value, 0 unlike an empty string, which ‘‘ 0 is a numeric value that ‘‘ represents a string of length 0 and null represents "null".

In other languages, there are also JavaScript-like null representations, such as Java, which is also used by null Swift nil , which is represented by Python None . However, in JavaScript, there is one and null similar undefined , which means "undefined".

The designer of JavaScript wants to null represent an empty value, whereas the undefined value is undefined. It turns out that there is no such thing as an egg, and the difference between the two is insignificant. In most cases, we should all use null . undefineduseful only when judging whether a function parameter is passed or not.

Array

An array is a set of sequentially arranged collections, each of which is called an element. An array of JavaScript can include any data type. For example:

NULL true];

The above array consists of 6 elements. Arrays [] are represented by , separate elements.

Another way to create an array is through a Array() function:

New // array created [1, 2, 3]

However, for the sake of readability of the code, it is strongly recommended to use it directly [] .

The elements of an array can be accessed through an index. Notice that the starting value of the index is 0 :

var NULL true ];arr[//  Returns an element with an index of 0, or 1//  Returns an element with an index of 5, which is true//  Index is out of range, return undefined

Object

A JavaScript object is a set of unordered collections of key-value, for example:

var person = {    ' Bob ',        Tags: [' js ', ' web ', ' mobile '],    ' Beijing ',    true,    null};

The key of a JavaScript object is a string type, and the value can be any data type. All of the above person objects define a total of 6 key-value pairs, each of which is also called an object's properties, for example, the property is person name ‘Bob‘ zipcode null .

To get the properties of an object, we use 对象变量.属性名 the following method:

// ' Bob ' // NULL

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Data types and variables in JavaScript