JavaScript Authority Guide Reading notes __java

JavaScript Authority Guide Reading notes The lexical structure of the first chapter

JavaScript is case-sensitive, while HTML is case-insensitive

The Unicode escape sequence is composed of/u as a prefix plus a 4-bit 16-digit number

Identifiers must begin with letters, underscores _, dollar characters $,

Semicolon: In JavaScript, a statement is exclusive, and you can usually omit the semicolon between statements.

Exception:

   1 return,break,continue, followed by a newline, JavaScript will fill in line at the semicolon.

   2. Binocular operator ++,--, if you want to be an expression suffix, you must be the same line as an expression.

chapter II types, values and variables

JavaScript supports decimal and hexadecimal, because the ECMAScript standard does not support octal direct, so it is best not to use 0 as a prefix of the direct amount

Properties of the Math object:

        Math.Round (. 6)   //=>1.0 rounded

        math.ceil (. 6)   //=>1.0 to go up

        Math.floor (. 6)   //=>0.0 go down the whole

Special case overflow in arithmetic operations (overflow): The result of a numeric operation exceeds the upper limit that JavaScript can represent

Positive numbers return Infinity, negative returns-infinity underflow (underflow): The result is smaller than the smallest number that JavaScript can represent, and returns 0,

Negative Underflow returns a special value of '-0 '

By 0 The whole out returns Infinity or-infinity, with the exception that 0/0 returns Nan

NaN: is not equal to any value, including itself

To judge the isNaN () function

        x!=x;  True only if X is Nan

0 and -0 values are equal except for the two values of the divisor.

Binary floating-point numbers do not accurately represent a simple number similar to 0.1

        (. 2-.1) = = (. 3-.2);  =>>false

String Direct: When you use single quotes to define a string, you need to be careful of all and abbreviations in English, with (/) escaping

JavaScript and HTML band? Use separate quote styles

JavaScript expressions use single quotes to represent strings

HTML event-handling properties are represented by double quotes in a string

Property:

        S.replace ("H", "H"); "Hello" => "Hello"

        s.touppercase ();//"Hello" => "Hello"

The string can also be used as a reading group, accessed by square brackets

Boolean value: Any value of JavaScript can be converted to a Boolean value

false:undefined; null; 0; -0; NaN; ' '

True: All other values, including all objects, array

Null is the key word for JavaScript, undefined is a predefined global variable, and "= =" thinks the two are equal

Wrapping Objects

        var s= "test";

        s.len=4;

        Var T=s.len; Undefined

    Behaves like an object when reading the properties (or methods) of strings, numbers, and Boolean values. But attempting to assign a value to its property ignores the action: the modification only occurs on the temporary object, and the temporary object is not persisted

The original value cannot be changed. (Undefined,null, Boolean, numeric, String)

Object can be changed by object property (array, function) two objects contain the same properties and values and are not equal

Number () and parsefloat () difference

Number (): Can only be used for decimal conversion, and no illegal trailing characters can appear

parseint (): Skips any number of leading spaces and ignores subsequent content, the first non-whitespace character is illegal, and the numeric direct quantity returns Nan

All objects converted to Boolean values are true

Although a global scope can write code without writing a var statement, you must use the VAR statement when declaring a local variable

Declaration advance: The function body local variables cover the same name global variables, the function body of the variable declaration will advance to the top of the function body

When you declare a JavaScript global variable, you are actually defining a property of the global object

In JavaScript, all columns are floating-point types, and the division result is also a floating-point third chapter

"= =": When both operand types and values are equal. 0===-0

' = = ': If two operands are not of the same type, an attempt is made to type conversions

The plus operator prefers strings; comparison operators prefer numbers, and only two numbers are string comparisons, and if one operand is Nan, the total returns false

In most cases a op= B is equivalent to A = a op b; It is not equivalent when a contains an expression with side effects, eg:data[i++]*=2; data[i++]=data[i++]*2;

typeof (NaN) = = "Number";

Delete can only delete object attributes or array elements, unlike the operand in C + + that deletes the entire object delete is not a left value, returns true without an operation, and returns true if the deletion succeeds