JS Basic Knowledge 2

First, the Prompt box 1. Pop-up Alert box alert ();   Window.alert (); Window Windows 2. Console output Console.log () 3. Documents Print Document document document.write (); 1. Which of the following JavaScript syntax formats is correct () A.                             echo "I enjoy JavaScript"; B document.write (I enjoy JavaScript) C.   Response.Write ("I enjoy JavaScript"); D  Alert ("I enjoy JavaScript"); Second, variable Java Var aa:int = 10; var num = 10; Letter _ $ begins with Var dd=100,ee=100 declares multiple variables comma-separated by 1.  In JavaScript, which of the following declaration variable statements is incorrect?   A, var aa; B, Var bb=3;  Cc= ' good ';  C, var dd = EE = 100;  D, var ff=3, gg= ' he ' s good '; Events three elements event source is triggered by the object noun event verb onclick onmouseover onmouseout event handler put the event source in the function.      event = function () {statement;} Entry function: window.onload = function () {} Four, inline<Divonclick= "alert (one)">Inline type outer chain type<Scripttype= "Text/javascript"src= "Xx.js"></Script> v. Data type number string Boolean null undefined 1.2 function function: The function is event-driven or A reusable code block that executes when it is invoked.  The four major inventions of the paper-making powder guide needle printing the Declaration function of the 1.2.1 function uses the same variables as the variable, you need to declare the 1.2.2 Custom Function fun () {alert ("I am a custom Function")}fun ();  The function does not call, itself does not execute the 1.2.3 function Direct Amount declaration var fun1 = function () {Alert ("Direct volume Declaration")}fun1 (); You also need to call 1.2.4 using the Function keyword to declare var fun2 = new Function ("var a = 10; var B = 20; Alert (A+B) "); Fun2 (); 1.2.5 Variable declaration promotes what is a variable boost 1 function fun () {2 console.log (num); 3 var num = 20;4} equals- --5 function Fun () {6 var num;7 console.log (num); 8 num = 20;9} inside the function body, declaring the variable will elevate the declaration to the top of the function body. Only the variable declaration is lifted, and no value is assigned.    var a = 18;f1 (); function F1 () {var b=9;    Console.log (a);    Console.log (b); var a = ' 123 ';} The result is: the undefined 9 1.2.6 function parameter arguments is a stored function that passed over the argument JavaScript creates a arguments object instance within the function while creating the function. The arguments object is only available when the function starts. The arguments object of a function is not an array and accesses a single parameter in the same way as an array element arguments the length of the object is determined by the number of arguments rather than the number of parameters <Script>    functionfn (A, b) {console.log (fn.length);//get the number of formal parameters that are functions        //console.log (arguments);Console.log (arguments.length);//The number of arguments is obtained        if(Fn.length==arguments.length) {Console.log (a+b); }        Else{console.error ("Sorry, your parameters do not match, the correct number of parameters is:" +fn.length); }        //Console.log (a+b);} fn (1,2); FN (1,2,3);</Script>  Var A = ten, B = 20;  The equivalent Var a = 10; var B = 20;1.3 Case Mouse display code: var box = document.getElementById ("box"); function fn (LIID,BG) {//package function parameter passed var obj =    document.getElementById (LIID);    Obj.onmouseover = function () {box.style.backgroundImage = BG; }}FN ("li01", "url (images/01big.jpg)"); Argument fn ("li02", "url (images/02big.jpg)"), FN ("li03", "url (images/03big.jpg)"), FN ("li04", "url (images/04big.jpg)"); FN ("li05", "url (images/05big.jpg)"); 1.4 returns value return definition: A function is actually a calculation process, and the result after the calculation is the return value. Defines the return value of a function: sets the return value with return inside the function, and a function can have only one return value. Also, terminate the execution of the code. All custom functions do not return a value by default, and do not wrap function $ (ID) {return document.getElementById (ID) after return;} $ ("demo"). Style.backgroundcolor = ' Purple '; $ ("test"). Style.backgroundcolor = "Blue"; 1. What is the result of the following code execution? Please analyze why?          1 var total=10;1 var number = Square (5), 2 alert (number), 3 function square (n) {4 total = n*n;5 Return total;6} result is 251.5 arithmetic operator +-*/% ^ = 2 5%2 = = 1 2%5 = = 2 2^3 A +     + + + Rear-facing  Each self-add 1 after the first operation after the ++a + + + each self plus 1 before adding the Operation 1. Analyze the code to get the correct results. 1 var a=10, b=20, c=30;2 ++a;3 a++;4 e=++a+ (++b) + (c + +) +a++;5 alert (e), 771.6-piece statement (IF) if (conditional expression  {statement;}  if () {}else {} if () else if () {} else if () {} else {}1.7 Get focus out of focus event we've learned the onclick before. Click onmouseover onmouseout '   Get Focus: onfocus FAO ~ gram dead loses focus: Onblur no Len ~ ~<Script>window.onload= function(){        vartxt=document.getElementById ("txt"); Txt.onfocus= function(){ //Get Focus            //alert ("Get Focus");            //when should I empty it?            //The user does not enter the time, the first time users use           //if the text inside the input is please enter ... Indicates that the user has not used, should be emptied            if(Txt.value== "Please enter ...") {Txt.value= ""; Txt.style.color= "#333"; }} Txt.onblur= function(){ //Lose Focus            //alert ("Lost Focus");            //When do we restore it?             //when the value of input is empty, we recover            if(Txt.value== "") {Txt.value= "Please enter ..."; Txt.style.color= "#ccc"; }        }    }</Script>1.8 This (own) refers to itself as this is primarily referred to as the caller of the event.    ClassName class Name $ ("result"). ClassName = "wrong"; InnerHTML replace the contents of the box with the text tag. Form Replacement Input.value IsNaN Nan is not a number      IS is not a number isNaN ("12") if the inside is not a number return true otherwise return false1.9 properties and methods the external properties of the iron of the 5.5-inch plastic of the phone black Property the color of the phone is black.     Iphone.color = "Red";     attribute to the value must be an equal sign method: Mobile phone to send text messages to play games chat QQ Watch movie verbs can do Iphone.tel ();  Methods and properties differ: methods are all enclosed in parentheses.    IsNaN ();   The verb method gives the value: IsNaN ("value"), the 1.9.1 form automatically obtains the focus Txt.focus (); Method onfocus Event<!DOCTYPE HTML><HTML><HeadLang= "en">    <MetaCharSet= "UTF-8">    <title></title>    <Script>window.onload= function(){            vartxt=document.getElementById ("txt"); Txt.focus (); //Get focus automatically        }    </Script></Head><Body>automatically get focus:<inputtype= "text"ID= "txt"/></Body></HTML>1.9.2 mouse over select form sele.onmouseover = function () {this.select ();//Select} method Select () Choose function 1.10 for loop life a loop i+=3 I=i+3 1.11 getElementsByTagName () Get a class of tags before we can get a box by ID get getElementById () only to a box we want to get some kind of tag like all  Div Li Spangetelementsbytagname (); Many of these are complex numbers and many get a pseudo-array. Lis Array lis[index number] one

JS Basics 2