JavaScript Note One

Introduction of a JavaScript method

<! DOCTYPE html>
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Index.js file
/* **created by Administrator on 2017/8/7. */ alert (123);
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Two JavaScript variables, constants, and identifiers
<!    DOCTYPE html>/*the class capacity of multi-line annotations*/        //the contents of a single line comment    //declaring a variable to assign a value      /*var i:i=10;      var j=20; */    //a row declares multiple variables so that each variable is separated    //var name= "Fang", age=18;    //JS A semicolon is a delimited symbol of a statement    /*var i=12;        var j=20;        alert (i);    Alert (j); */    //If a variable is declared unassigned only, it will print out Undefind    /*var x;        alert (x);        var n=10;    var n=3.1415926; */</script>View Code
Three JS data types
<!    DOCTYPE html>/*var i=100.89;        var s1= "Hello";        var B=false;   Console.log (typeof i);   Number Console.log (typeof S1);   String Console.log (typeof B); Booleam*//*var arr=[111,222, "Hello"];      var obj={"name": "Egon", "Age": "N"} var obj2={name: "Fang", Age: "" "} Console.log (typeof arr);    Object Console.log (typeof obj);    Object Console.log (obj["name"]);           Object Console.log (obj);        Object Console.log (OBJ2); *///undefined:1 When a variable only declares an unassigned value to the return value of Undefined;            //2 When a function does not return a value, a undefined value is returned by default.    /*var A;       Console.log (a);    Undefined Console.log (typeof a); Undefined*///var a=null;//Console.log (a); Null//Console.log (typeof a); Object        //The nan value belongs to the number type: When a string is encountered that is not valid, a Nan data is obtained    varS= "Fang"; varret2=+R;   Console.log (Ret2); //NaNConsole.log (typeofRet2)// Number</script>View Code
Four-Boolean type
<! DOCTYPE html>        console.log (true+2);        Console.log (false+2);         if (1) {            Console.log ("OK");        }     </script>
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Five operators
<!    DOCTYPE html>//x + + ++x<!--varX=10;--> <!--x+=1;-->//x + +: Assign values first in the calculation<!--varret=x++;//x + + (x=x+1)-        //++x First calculated and then assigned value<!--varRet1=++x;//++x (x=x+1)--<!--console.log (x);--> <!--console.log (ret);--> <!--console.log (RET1);-->//   ===  !==<!--Console.log (2=== "2");-->//!  && | | Logical OR with non-<!--varName= "Egon";--> <!--vargender= "Male";--> <!--if(name== "Egon" && gender== "males") {--> <!--console.log ("success!"); -<!--}-->//+: string concatenationConsole.log ("Hello" + "world"); Console.log ("Hello" +234); </script>View Code
Six-Process Control
<!    DOCTYPE html>/*//if expression;  Pass//JS if statement//double branch if (expression) {EXECUTE statement}//Multi-branch statement if (expression)                {EXECUTE statement} else if (expression) {EXECUTE statement} else { Execute statement}*//*//exercise: Var num=67; if (num>90) {alert ("excellent")} else if (num>80) {alert ("benign")} else if (num>60) {Alert ("pass")} else {alert ("Failed")}*///Switch Case Statement /*var week=3;            Switch (week) {case 1:console.log ("Monday");            Case 2:console.log ("Tuesday");            Case 3:console.log ("Wednesday");            Case 4:console.log ("Thursday");            Case 5:console.log ("Friday");            Case 6:console.log ("Saturday");        Case 7:console.log ("Sunday"); }        */ //For Loop: //For Loop mode 1: Conditional loop (highly recommended)/*For (Var i=0;i<10;i++) {Console.log (i); }*///For Loop mode 2: Traversing loops/*var arr=[111,222,333]; for (var i in arr) {Console.log (i,arr[i])}*/<!--//While Loop --<!-- while(expression) {--> <!--loop Body--<!--}--> <!--varCount=0;--> <!--varSum=0;--> <!-- while(count<101) {--> <!--sum+=count;--> <!--count++;--> <!--}--> <!--c Onsole.log (sum);-->varSum2=0;  for(vari=0;i<101;i++) {sum2+=i;            } console.log (SUM2); //Break exits the entire loop, continue exits when the secondary loop</script>View Code
Seven String objects
<!    DOCTYPE html>vars= "Hello World"; //Console.log (s.length);Console.log (S.charat (4)); Console.log (S.lastindexof (L)); Console.log (S.indexof (L)); Console.log (S.substr (3,4));//Lo WConsole.log (s.substring (3,4));//l Gu Tou disregard the tailConsole.log (S.concat ("Egon")); </script>View Code
JavaScript Note One