JavaScript Knowledge Summary------JS easy to ignore details (continuous update)

• In operator

Syntax: boolean "name" in object to determine whether an object has a property

var myObject = {name: ' ng small bits '};console.log (in//true   A return value of TRUE indicates that the name attribute in //False is present in MyObject the   return value is false to indicate that the Name property does not exist in MyObject

• New operator and direct volume (literal)

var objone = {};   // Direct Volume (literal) generation of objects var New Object ();   // The new operator generates the object

• Reference types and value types

value type assignment does not change the original data reference type in memory is one, the value change will change the previous data

varNUM1 = ' 13 ';varnum2 =num1;num2= ' 23 '; Console.log (NUM1)//13 Change Value num2 value NUM1 has not changed, proving that NUM1 and num2 in space respectively occupy their own memory, is two independent individualsConsole.log (NUM2)// atConsole.log (NUM1 = = num2);//false Here is a value reference comparison, so only the comparison value is the samevarObj1 = {name: ' Wu Xiao Broken ', age:18};varObj2 =Obj1;obj2.sex= ' Male 'Console.log (OBJ2); //{name: "Wu Xiao", age:18, Sex: "Male"}Console.log (OBJ1);//{name: "Wu Xiao", age:18, Sex: "Male"} when the Obj2 attribute is added, the obj1 changesConsole.log (obj1 = = obj2);//True reference type common one memory, equivalent to Obj2 is obj1 desktop shortcut, obj1 and Obj2 point to the same memory path

• Delete

1. To delete an element in an array
2. Properties or methods of an object
3. Delete a variable declared with no Var

varARR1 = [1,2,3,4]DeleteArr1[0]console.log (ARR1); //[Empty, 2, 3, 4] length unchanged, just remove the valuevarobj = {name: ' Wu Xiao, age:18 '};Deleteobj.nameconsole.log (obj)//{age:18} Delete key value pairsvarA1 = ' Test ';DeleteA1;console.log (A1);//Test variable A1 still exists, A1 not deletedA2= ' Test ';DeleteA2;console.log (A2)//uncaught REFERENCEERROR:A2 is not defined proves that the variable has been deleted A2

• Error handling methods

try{ possible error code } catch (e) { e-> received error message }finally{ No matter how it will be last executed }

Try {    //code that may be wrong    //1.Obj.name;//system error Message->obj is not defined    //2.    //throw new error (' I am an error message '); Forcibly throw out an error message}Catch(Error) {//error message thrown if an error is executed Error->tryConsole.log (Error);//referenceerror:a is not defined}finally {    //no matter how it's going to lastConsole.log (' Finally executed me? ‘);//Did I end up doing it? }

• JS execution: Pre-parse (function, and Var), one sentence to execute

parsing Order: SCIRPT code block, VAR, parsing execution Environment | | function (function precedence above Var)

<script>    console.log (msg); // with the below MSG definition variable exists in two blocks of code therefore: uncaught referenceerror:msgis not defined </script><script>    var msg = ' Wu Xiao Broken ' </script><script>    console.log (msg);    // msg in the last code to complete the quick parse, so print out: Wu Small broken    Console.log (MSG1);  // with MSG1 exists with the same code block, the parsing execution environment exists within a script code block so: undefined    var msg1 = ' Wu Xiao Broken ' </script>

• An expression

An

expression that has a value in relation to data and operators

.

• Statement

expression + semi-colon

JavaScript Knowledge Summary------JS easy to ignore details (continuous update)