The so-called closure should mean that the internal function reads a variable other than the current function, that is, the context in which it was created.
Copy Code code as follows:
function Hello () {
var char = "Hello,world";
function print () {
Console.log (char);
};
return print ();
}
Note that the print function here refers to the char variable of the external Hello function, so here we can return a
Copy Code code as follows:
This function, in a sense, should be attributed to the scope. Of course, we have no way to directly access char unless we make a mistake when declaring the variable. Such as
Copy Code code as follows:
function Hello () {
char = "Hello,world";
function print () {
Console.log (char);
};
return print ();
}
Just because of the lack of a var.
Copy Code code as follows:
Here, hello turns into a closed bag. Closures are a special kind of object. It consists of two parts: a function, and the environment in which the function is created. The environment consists of any local variables that are in the scope when the closure is created.
Javscript closure and this
Note that it may be problematic to read this and arguments.
Copy Code code as follows:
function Hello () {
This.char = "Hello,world";
function output () {
char = "I ' m no Hello World";
Console.log (This.char);
};
return output ();
}
Of course, this example is not appropriate, so, we need an additional example to explain this problem, the following reference to a "JavaScript advanced programming," an example to illustrate this problem.
Copy Code code as follows:
var name = "the window";
var object = {
Name: "My Object",
Getnamefunc:function () {
return function () {
return this.name;
}
}
};
Object.getnamefunc () ()
It's just that usage, and the solution is to save a temporary variable that, as in the previous article on some knowledge of this one about JavaScript.
Copy Code code as follows:
var name = "the window";
var object = {
Name: "My Object",
Getnamefunc:function () {
var that = this;
return function () {
return that.name;
}
}
};
Object.getnamefunc () ()
javscript Closures and read-write variables
It is noteworthy that we can modify these variables if we do not handle our variables well.
Copy Code code as follows:
function Hello () {
var char = "Hello,world";
return{
Set:function (String) {
return char = string;
},
Print:function () {
Console.log (char)
}
}
}
var say = hello ();
Say.set (' New Hello,world ')
Say.print ()//New Hello World
Javascript Closures and performance
References to MDC
Copy Code code as follows:
It would be unwise to create functions in other functions without the need for some special tasks, as closures have a negative impact on script performance, including processing speed and memory consumption.
The article also said.
Copy Code code as follows:
For example, when you create a new object or class, the method should usually be associated with the object's prototype, rather than the object's constructor. The reason is that this will cause each constructor to be invoked and the method will be assignable once (that is, for each object creation).
