Javascip-basic--- Notes for details:
1. Special values: Nan, infinity, isnan (), isfinite ()
NAN:
VaRA = parseint ('a123'); Window. Alert ();//Output Nan
Infinity:
Window. Alert (6/0); // output infinity (it is better not to write this)
Isnan (): determines whether it is a number. If it is not a number, true is returned. If it is a number, false is returned.
VaRA = "DD"; Window. Alert (isnan ());//Returns true.
Isfinite ():Used to determine whether it is infinite.If number is Nan (not a number) or positive or negative infinity, false is returned.
Window. Alert (isfinite (6/1); // returns truewindow. Alert (isfinite (6/0); // returns false
2. logical operators:
In logical operations,0,"",False,Null,Undefined,NanBoth representFalse
(Or |)| Returns the value of the first value not false (the object can also be), or the last value (if all values are false)
This knowledge point is widely used in Javascript frameworks.
A,
VaRA =True;VaRB =False;VaRC = B |A; window. Alert (C );//Output True
B,
VaRA = 2;VaRB = 0VaRC = A |B; window. Alert (C );//Returns the first value and outputs 2.
C,
VaRA =False;VaRB ="";VaRC = 0;VaRD =NewObject ();//ObjectVaRAA = A | B | c | D;//A, B, and C are all false. This Returns D.Window. Alert (AA );//Returns D (object)
4. multi-branch Switch
var flag = 1 ; switch (FLAG) { default : window. alert ( "none of them" ); case 'A' : window. alert ( "A" ); case 'B' : window. alert ( "B"); /// no break statement, no match is successful, and all results are output } VaRFlag = 1;Switch(FLAG ){Default: Window. Alert ("Nothing");Case'A': Window. Alert ("");Case1: Window. Alert ("B ");// No break statement. If the match is successful, the break statement is no longer found. At this time, B is output.}
5. function call
Func. js
FunctionABC (VAL) {window. Alert ("ABC ()" +Val );}//Functions with return valuesFunctionTest (num1, num2 ){VaRRes = 0; Res= Num1 +Num2;ReturnRes ;}//Functions without return valuesFunctionNoval (num1, num2 ){VaRRes = 0; Res= Num1 +Num2 ;}
Function call:
<HTML> <SCRIPT type = "text/JavaScript" src = "func. js"> </SCRIPT> <SCRIPT type = "text/JavaScript"> // Function call 1 --- common call (common call function) ABC (50 ); // Function call 2 --- Variable = function nameWhen calling:Variable (actual parameter) VaR Test1 = ABC; // In this case, the variable is equivalent to the reference (pointer) of the function) Window. Alert (ABC ); // Output the entire ABC FunctionCode, You can understand Test1 (500 ); // If the called function has a return value, you canProgramIs returned directly, no return value is returned, but you have received it, this is returned undefined // Call a function with a returned value VaR Res = test (20, 40 ); Window. Alert (RES ); // Call a function without a return value Window. Alert ("calling a function without return values" ); VaR Res = noval (1, 1); // Output undefined Window. Alert (RES ); </SCRIPT>
JS supports functions with Variable Parameter count
<HTML> // Function call-recursion /* Function ABC (Num) {If (Num> 3) {ABC (-- num);} document. writeln (Num);} // call the function ABC (5); // output 3 3 4 */ // JS supports functions with Variable Parameter count Function ABC (){ // JS provides an arguments that can access the input value. Window. Alert (arguments. Length ); // Number of incoming records // Traverse input parameters For ( VaR I = 0; I <arguments. length; I ++ ) {Window. Alert (arguments [I]) ;}} // Call Window. Alert ("ABC (12,13, \" Hello \ ", 56 )" ); ABC ( 12, 13, "hello", 56 ) Window. Alert ( "ABC (5 )" ); ABC ( 5 ); Window. Alert ( "ABC ()" ); ABC (); </SCRIPT>
Use global variables and local variables in the function
<SCRIPT type = "text/JavaScript">//Global variables and local variablesVaRNum = 90;FunctionTest (){//In a function, if VaR is not included, global variables are used,//If VaR is included, a new num variable is defined in the function.//VaR num = 900;Num = 900;} Test (); window. Alert ("Num =" + num );//Output num = 900.</SCRIPT>
6. There are two methods to access object attributes
<SCRIPT type = "text/JavaScript">/* // In JS, everything is the object function person () {} window. alert (person. constructor); var A = new person (); window. alert (. constructor); window. alert (typeof A); window. alert (person ); */ // There are two ways to access object attributes: 1. Object Name. attribute name 2. Object Name ["attribute name"] (dynamic call) Function Person (){} VaR A = New Person () A. Name = "James" ; Window. Alert (A. Name ); // Normal Mode VaR STR = "Na" + "me" ; Window. Alert (A [STR]); // Dynamic Mode // Window. Alert (A ["name"]); // output James </SCRIPT>
7,There are five ways to create an object
- Factory method-use new object to create an object and add relevant properties.
- Use constructors to define classes (prototype objects ).
- Use prototype
- Constructor and prototype hybrid mode.
- Dynamic prototype.
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