Js use of the common part of the grammar class literal numeric string Boolean operator undefind null Nan

js in use:

data verification

Read and write HTML elements

Interact with the browser effect

Netnew

web game production

Programming Node.js server-based technology

javascript part

Common usage of grammar

alert popup: . window.alert () method of the object ()

Writing directly parentheses behind the alert, content inside parentheses written text, text wrapped in double quotes.

console.log (): the console is a console panel output content js built-in object.

(Typeof) data detection

Switch number string +: + when both sides are represented by the digital adder Literals

When both sides are not both number + type, and in particular, numeric string writing, + represents a splicing action.

prompt (): 2 parameter prompt text box

1 Parameters: prompt text

2 parameters: default text

The string into number method: parseInt () integer, parseFloat () float (camelCase)

parseInt (): rounding

parseFloat (): Float

	parseInt()：  将字符串转为整数
1	// 参数：书写字符串
2	console.log(parseInt("12.1212"));
3	console.log(parseInt("2333e10"));
4	console.log(parseInt("2333a10"));
 
	结果有可能是NaN
1	console.log(parseInt("a12"));
2	console.log(parseInt("十二"));
3	console.log(parseInt("你好"));

Literal Category: number, string, Boolean value, undefined, null

Any data have data type, such as numbers, strings, arrays, functions, etc.

Data type name:

Simple data types:

number: integer, float, special value

string: String

boolean: true , false

undefined: undefined value contains only one data type number of data types are number Nan

Reference data types:

object (the object)

function (function)

Digital: integer, float, special value

Integer representation: decimal, octal, hexadecimal

Octal: 0,0o, 0O (every eight into a) significant figures 0-7

Hex: 0x, 0X (every hex a) 0-9 af effective than direct digital error

Float: a decimal representation only

Special value:

i nFinity: Due to computer capability effectively, displaying endless Infinity (very large number) exceeds the limit

NaN(not a number)

String

String literal: refers to the variety of life say the words. For example, in various languages, the language of some numbers, punctuation, etc.

String literal: ""

Declare variables:

Variable names (identifiers) naming rules:

The first character can be letters (js case-sensitive), down the line (_), dollar sign $ followed by characters can be letters, _, $, digital

You can not be a keyword or reserved word

Keywords: js have some words functionality.

Reserved words: There are no special features, the future may be retained keywords

Keywords:

break　　do　　instanceof　　typeof　　case　　else　　new　　var　　catch　　finally　　return　　void　　continue　　for　　switch　　while　debugger*　　 function　　this　　with　　　　default　　if　　throw　　delete　　in　　try　

Reserved words:

abstract　　enum　　int　　short　　boolean　　export　　interface　　static　　byte　　extends　　long　　super　　char　　final　　native　　class

synchronized　　float　　package　　throws　　const　　goto　　private　　transient　　debugger　　implements　　protected　　volatile　　double　　

import　　public

Operators

+, -, *, /,% (remainder) modulo the first integer direct multiplication and division count, modulo, and then count subtraction, if there are parentheses in parentheses operator

Pure numeric string involved in computing, a pure numeric string without writing parseInt (), parseFloat (),

// 参数只有一个字符串，不用书写进制参数
	// 检测数据类型
	console.log(typeof(parseFloat("12.12.1.22444")));
	console.log(parseFloat("12.12.1.22444"));
	// 浮点数可以使用幂
	console.log(parseFloat("1.2e-4"));
	// 结果也有可能是NaN
	console.log(parseFloat("你好12"));


number
12.12
0.00012
Nan

Automatically determining implicitly converted into corresponding digital involved in computing. (Except for the addition, the addition is still mosaic effect)


	// 纯数字字符串，会隐式转换,加法除外，还是拼接作用
	console.log(12 - "2");
	console.log(12 * "2");
	console.log(12 / "2");
	console.log(12 % "2");
	console.log(12 + "2");


10
24
6
0
122

Infinity involved in computing

// Infinity
	console.log(12 + Infinity);
	console.log(12 - Infinity);
	console.log(12 / Infinity);
	console.log(12 % Infinity);

Infinity
-Infinity
0
12

NaN result is NaN


	// NaN运算
	console.log(12 + NaN);
	console.log(12 / NaN);

undefined involved in computing the result is NaN

// undefined参与运算结果都是NaN
	console.log(12 + undefined);
	console.log(12 - undefined);
	console.log(12 * undefined);

Non-pure numeric string involved in computing the result is NaN, + or mosaic effect

	// 非纯数字字符串参与运算，结果都是NaN，+ 还是拼接作用
	console.log(12 - "你好");
	console.log(12 * "你好");
	console.log(12 + "你好");

NAN
NAN
12你好

true, false, null, will be involved in computing implicit conversion. (Addition implicitly converted)

true 1

false 0

null 0

        console.log(12 + true);
	console.log(12 - false);
	console.log(12 * null);
	console.log(12 / null);



12+1=13
12-1=11
12*0=0
12/0=Infinity