22 strict mode & this keyword

Strict mode:

The new directive after ECMA5: "use strict"

It is not a statement, but a text expression, an earlier version of JavaScript will ignore it.

Strict mode can not use an undeclared variable.

 

Strict mode features:

• Inside the function declaration strict mode, with local scope. Only the internal function code is executed in accordance with strict mode.
• Do not allow the use of objects that are not declared
• Objects can not be deleted
• Function can not be deleted
• Repeat function parameter names are not allowed
• Octal values ​​do not allow text and escape character
• Allowed to write read-only property, only the properties acquired evil
• Not allowed to delete not delete attributes such as prototype
• Does not allow for the future reserved keyword
• In strict mode, the function of this is undefined

 

this Keywords: depending on the location of its use, it belongs referents

• Method, refer to the owner of the object (in JavaScript function generally invoked by the function name, and the method is invoked by the object function)
• The individual case, refers to the global object (object Window)
• Function, refer to a global object
• Function, strict mode, this is undefined
• Event, this refers to the generation of HTML elements receive events
• Such a method call () and apply () may be any object to this reference

< Script > 
// create objects 
var Person = { 
    name: " Lisi " , 
    Age: 18 is , 
    the fullName: function () {
         return  the this .name +  "  "  +  the this .age; 
    } 
}; 

// display the data objects 
/ / the method of this method refers to the owner of the object, person.fullName this () refers to the person object 
document.getElementById ( " Demo " ) .innerHTML = person.fullName ();

< Script > 
// strict mode, the function of this is undefined 
" use strict " ; 
document.getElementById ( " Demo " ) .innerHTML = myFunction ();
 function myFunction () {
   return  this ; 
} 
</ Script >

<! - in HTML event, this refers to the HTML element receives this event -> 
    < the Button onclick = "this.style.display = 'none'" > point I disappear </ the Button >

< Script > 
// Call this target will point to the parameters passed in the object, so the call is person2 variables. 
var PERSON1 = { 
    the fullName: function () {
         return  the this .name +  "  "  +  the this .age; 
    } 
} 
var PERSON2 = { 
    name: " Lisi " , 
    Age: 2 
} 
Alert (person1.fullName.call (PERSON2)); 
</ Script >

 

 

 

 

 

 

Strict mode advantages:

• It makes it easier to write JavaScript security
• Before the acceptable bad grammar into a real error
• In general JavaScript, hit the wrong variable name creates a new global variable in strict mode throws an error, can not be created.
• In general JavaScript, if not the assignment to write property, the developer will not get any error feedback.
• In strict mode, the non-writable, read-only, there is no property assignment, or assign a value to a variable or an object that does not exist, it will throw an error,