JS You may not know some of the points of knowledge (i)

1, JS program is written in the Unicode character set,

2. Escape character: Backslash

function Test () {   var s= ' you\ ' re right,it can\ ' t be a quote ';   Console.log (s);}

3. Slice method: Method to return the selected element from an existing array arrayobject.slice (Start,end)

Start required if it is a negative number, it specifies the position from the end of the array. In other words, 1 refers to the last element, 2 refers to the second-lowest element, and so on.
End optional specifies where to end the selection

function Test () {    var arr = new Array (3);    Arr[0] = "George";    ARR[1] = "John";    ARR[2] = "Thomas";    ARR[3] = "James";    ARR[4] = "Adrew";    ARR[5] = "Martin";    var s= "Hello World";    document.write (Arr.slice (1) + "<br/>")    document.write (Arr.slice (2, 4) + "<br/>")    document.write (S.slice (1, 4) + "<br/>")    document.write (S.slice ( -3) + "<br/>")}

Results:

John,thomas,james,adrew,martin
Thomas,james
Ell
Rld

4. The original value of JS species (Undefined,null, Boolean, number, string)

function Test () {    var s = "Test";    var s1= "test";    if (S===S1) {}//true}

Reference type: Object, array

function Test () {   var o={x:1};   var p={x:1};   if (o===p) {}//false   var a=[1,2,3];   var b=[1,2,3];   if (a===b) {};//false   var c=[];   var d=c;   B[0]=1;   if (C==d) {};//true}

5. Type conversion

   Boolean   //undefined-> "undefined"->nan->false   //null-> "null"->0- >false   //true-> "true"->1->true   //false-> "false"->0->false   //"" (empty string), "->0->flase   //" 1.2 "(non-empty, digital)," 1.2 "   ->1.2->true//" One "(non-null, non-digital)," one "->nan-> True   //0-> "0"->0->false   //nan-> "NaN"->nan->flase   //1-> "1"->1->true

6. Operators

1) in operator

function Test () {     var o={x:1,y:2};    The left is a string or can be converted to a string, the right is an object, the left property exists on the right side of the object, then return OK if ("    x" in O) {}//true if ("    z" in O) {}//false if ("    toString" in O {}//true, object inherits the ToString method}

2) instanceof

    var d=new Data ();    if (d instanceof date) {}//true The Left object is an instance of the right class, returns True    if (z instanceof date) {}//false

3) Delete

function Test () {     var o={x:1,y:2};    Delete o.x;    if ("X" in O) {}//false}

7. For in

function Test () {     var o={x:1,y:2};    For (i in O) {        console.log (o[i]);}    }

8. Try: Catch.. Finally

function Test () {     try{        var n=number (Prompt ("Please enter a positive integer"));        var f=factorial (n);        Alert (n+ "! =" +f);    }    catch (ex) {        alert (ex);    }    finally{        Aler ("show" whether or not there is an exception);    }}function factorial (x) {     if (x<0) {        throw new Error ("X cannot be negative");    }    if (IsNaN (x)) {        throw new Error ("You are not entering a number");    }    for (Var f=1;x>1;x--) {        f*=x;    }    return F; }

9. Width statement

function Test () {    //Document.forms[0].username.value = "AA";    Document.forms[0].pwd.value = "AA";    Document.forms[0].qq.value = "AA";    Document.forms[0].realname.value = "AA";    Document.forms[0].tel.value = "AA";    Simplified mode with    (Document.forms[0]) {        username.value= "AA";        Pwd.value= "AA";        Qq.value= "AA";        Tel.value= "AA";        Realname.value= "AA";    }}

　　

　

　　

JS You may not know some of the points of knowledge (i)